ffiCAL  BOTANY 


GIFT  OF 


PRACTICAL  BOTANY 


BY 

JOSEPH  Y.  BERGEN,  A.M. 

AUTHOR  OF  "ELEMENTS  OF  BOTANY,"  "FOUNDATIONS  OF  BOTANY" 
"  PRIMER  OF  DARWINISM,"  ETC. 


OTIS  W.  CALDWELL,'PH,IX     •  « '•""•  V-  ,'*? 

AUTHOR  OF  "PLANT  MORPHOLOGY"  AND  « LABORATORY  M?A£M?Ai,  ojf»B»T)A»V$ 

ASSOCIATE  PROFESSOR  OF  BOTANY  IN  THE  SCHOOL  OF  EDUCATION 

UNIVERSITY  OF  CHICAGO 


GINN  AND  COMPANY 

BOSTON     •     NEW    YORK     •     CHICAGO     •     LONDON 
ATLANTA     -     DALLAS     •     COLUMBUS     •     SAN    FRANCISCO 


',,'  ',  ',  ENTERED  AT  STATIONERS'  HALL 


r  COPYRIGHT,  1911,  BY 
:  BERGEN  AND  OTIS  W.  CALDWELL 


ALL   RIGHTS    RESERVED 

021.10 


gftc  fltftenaeum 

GINN  AND  COMPANY  •  PRO- 
PRIETORS •  BOSTON  •  U.S.A. 


PREFACE 

There  are  already  so  many  books  embodying  elementary 
courses  in  botany  that  whoever  offers  another  should  give 
reasons  for  so  doing.  As  here  set  forth,  the  study  of  plants 
is  related  to  everyday  life  more  closely  than  is  usually  done. 
Those  aspects  of  plant  life  are  presented  which  have  the 
largest  significance  to  the  public  in  general,  and  which  are 
of  interest  and  educative  value  to  beginning  students.  The 
book  includes  the  principles  of  plant  nutrition,  the  relation  of 
plant  nutrition  to  soils  and  climate  and  to  the  food  of  animals 
and  men ;  it  discusses  some  of  those  diseases  of  plants,  ani- 
mals, and  men,  which  are  produced  by  parasitic  plants ;  the 
propagation  of  plants,  plant  breeding,  forestry,  and  the  main 
uses  of  plants  and  plant  products  are  given  in  an  elementary 
way.  The  elements  of  plant  life  and  structure  are  presented 
synthetically  rather  than  by  use  of  the  special  divisions  of 
botanical  study,  which  are  more  helpful  to  advanced  students 
than  to  beginners.  It  is  believed  that  this  mode  of  treatment 
stimulates  and  develops  a  scientific  method  of  thinking  by 
directing  attention  to  the  plant  as  a  living  unit  and  a  citizen 
of  the  plant  world.  No  attempt  is  made  to  include  references 
to  such  recent  discoveries  in  the  field  of  botany  as  are  botani- 
cally  significant  but  not  important  for  elementary  instruction. 

Chapters  I  and  II  are  so  arranged  that  a  student  may  secure 
a  general  introductory  appreciation  of  the  significance  of  plant 
structure  and  work.  It  is  intended  that  Chapter  I  should  be 
used  as  a  means  of  raising  questions  concerning  the  place  of 
plants  in  nature.  Chapter  II  presents  an  outline  of  the  five 
dominant  structures  of  seed  plants,  and  the  kind  of  work  that 
is  done  by  each.  It  is  intended  that  this  chapter  shall  enable  the 
student  to  see  the  plant  as  a  working  unit,  while  the  chapters 

iii 


iv  PRACTICAL  BOTANY 

following  it  give  a  more  detailed  treatment  of  each  of  the 
dominant  structures,  and  the  outline  sketch  of  the  whole  plant 
now  serves  as  the  basis  of  interpretation  of  this  more  special 
study.  Then  follow  rather  brief  though  adequate  chapters 
dealing  with  the  great  groups  in  the  order  of  their  increasing 
complexity,  and  these  are  followed  by  chapters  which  treat  of 
broad  aspects  of  plants  and  their  relation  to  plant  industries. 

The  material  in  the  book,  which  is  sufficient  for  a  year's 
course,  is  so  arranged  that  it  can  be  adjusted  to  a  half-year 
course  when  local  needs  make  this  desirable.  When  seasons  are 
favorable  it  is  thought  best  to  follow  the  order  of  chapters 
as  given,  but  seasonal  conditions  are  so  diverse  in  different 
parts  of  the  country  that  the  teacher  is  urged  to  rearrange 
chapters  whenever  necessary  for  adequate  illustration  of  such 
topics  as  flowers,  seeds,  and  weeds.  If  this  is  done,  Chapters  I 
and  II  may  be  studied  briefly,  and  then  followed  by  chapters 
dealing  with  special  topics. 

When  the  book  is  used  in  a  half-year  course,  Chapters  I 
and  II  should  constitute  an  introduction,  and  it  will  usually 
be  found  advisable  to  follow  these  with  Chapters  III-XI  and 
XXI-XXV.  In  some  cases,  however,  it  will  be  found  advis- 
able to  follow  Chapters  I  and  II  with  Chapters  X~XX.  In 
any  event,  in  a  half-year  course,  Chapters  XXI-XXV,  be- 
cause of  their  practical  significance,  should  be  assigned  for 
collateral  reading  if  they  are  not  used  as  the  basis  of  regular 
class  work. 

Not  infrequently  facts  are  restated  in  connection  with  topics 
other  than  those  with  which  they  first  appear.  This  seems  un- 
avoidable unless  other  important  considerations  are  sacrificed, 
such  as  securing  plasticity  in  the  order  of  use  of  the  various 
chapters  and  avoiding  excessive  cross  reference. 

The  number  of  botanical  terms  used  is  as  small  as  is  con- 
sistent with  a  clear  presentation  of  the  facts.  The  order  of 
the  great  groups  of  plants  agrees  with  the  most  recent  usage 
of  the  best  botanists.  In  accordance  with  this  usage  the  bac- 
teria and  the  blue-green  algae  are  presented  first  in  the  studies 


PREFACE  V 

of  the  great  groups.  The  relatively  large  importance  to  general 
students  of  a  knowledge  of  bacteria  justifies  the  considerable 
amount  of  space  that  is  given  to  this  group. 

The  course  outlined  in  this  book  will  meet  the  needs  of 
students  who  wish  to  present  botany  for  college  entrance. 
While  the  point  of  view  is  somewhat  different  from  that  which 
is  usual  in  elementary  textbooks  of  botany,  the  topics  treated 
are  those  outlined  for  secondary  schools  by  the  Botanical  Soci- 
ety of  America  and  the  North  Central  Association  of  Colleges 
and  Secondary  Schools.  These  units  are  the  ones  generally 
recognized  throughout  the  United  States. 

The  authors  wish  heartily  to  recognize  the  valuable  assist- 
ance that  has  been  rendered  them  by  the  following  authori- 
ties :  Professor  Henry  C.  Cowles,  Mr.  George  D.  Fuller,  and 
Professor  Edwin  O.  Jordan,  of  The  University  of  Chicago; 
Professor  Benjamin  M.  Davis,  of  Miami  University ;  Professor 
William  F.  Ganong,  of  Smith  College;  Director  Charles  E. 
Thorne,  Botanist  Augustine  D.  Selby,  and  Agronomist  C.  G. 
Williams,  of  the  Ohio  Agricultural  Experiment  Station ;  Act- 
ing Director  Herbert  J.  Webber  and  Professor  C.  G.  Warren, 
of  the  New  York  State  College  of  Agriculture ;  and  Professor 
Edgar  N.Transeau,  of  the  Eastern  Illinois  State  Normal  School. 

A  large  number  of  high-school  teachers  of  botany  have 
given  suggestions  and  criticisms,  and  we  desire  to  express 
our  appreciation  of  this  assistance  from  those  who  are  in 
direct  contact  with  the  problems  of  teaching  botany  in  sec- 
oiidary  schools.  Mr.  William  L.  Eikenberry,  of  the  University 
High  School,  Chicago,  has  given  abundantly  of  his  experience 
and  his  time  in  making  suggestions  and  reading  manuscript 
and  proof.  Mr.  Paul  T.  Sargent,  Mr.  E.  N.  Fischer,  and 
Mr.  F.  Schuyler  Mathews,  the  illustrators,  have  added  to 
their  artistic  ability  a  genuine  interest  in  the  presentation  of 
plant  life  to  beginning  students,  for  which  we  wish  to  express 
our  appreciation. 

JOSEPH  Y.  BERGEN 
OTIS  W.  CALDWELL 


CONTENTS 

CHAPTER  PAGE 

I.  INTRODUCTORY — PLANTS  IN  NATURE 1 

II.  GENERAL  STRUCTURE  AND  WORK  OF  PLANTS  ....  5 

III.  ROOTS ,     .     .     .  24 

IV.  THE  STEM  AND  THE  LEAF 39 

V.  UNDERGROUND  STEMS;  STORAGE  IN  STEMS  AND  LEAVES; 

REPRODUCTION 72 

VI.  BUDS  AND  BRANCHES 90 

VII.  FLOWERS 104 

VIII.  POLLINATION  AND  FERTILIZATION 115 

IX.  SEEDS  AND  SEEDLINGS;  SEED  DISTRIBUTION    ....  136 

X.  THE  GREAT  GROUPS  OF  PLANTS 156 

XL  THE  BACTERIA  (SCHIZOMYCETES) 161 

XII.  THE  BLUE-GREEN  ALG^E  (CYANOPHYCE*:) 180 

XIII.  THE  GREEN  ALG^E  (CHLOROPHYCE*:)  AND  OTHER  ALG^C  188 

XIV.  THE  ALG^-FUNGI  (PHYCOMYCETES) 213 

XV.  THE  SAC  FUNGI  (ASCOMYCETES)  ;   THE  LICHENS;  THE 

BASIDIUM  FUNGI  (BASIDIOMYCETES) 226 

XVI.  MOSSES  AND  LIVERWORTS  (BRYOPHYTES) 257 

XVII.  THE  PTERIDOPHYTES 274 

XVIII.  GYMNOSPERMS 299 

XIX.  ANGIOSPERMS 321 

XX.  SOME  LEADING  FAMILIES  OF  FLOWERING  PLANTS  AND 

v             THEIR  USES 335 

XXI.  FURTHER  DISCUSSION  OF  DEPENDENT  PLANTS      .     .     .  371 

XXII.  TIMBER:  FORESTRY 390 

XXIII.  PLANT  BREEDING .     .     ...     .  412 

XXIV.  FURTHER  DISCUSSION  OF  PLANT  INDUSTRIES  ....  434 
XXV.  WEEDS 465 

XXVI.  ECOLOGICAL    GROUPS  ;    REGIONAL    DISTRIBUTION    OF 

PLANTS 477 

APPENDIX 515 

GLOSSARY 520 

533 

vii 


PRACTICAL  BOTANY 

CHAPTER  I 
INTRODUCTORY  — PLANTS  IN  NATURE 

1.  Abundance  and  distribution  of  plants.  We  are  so  accus- 
tomed to  the  presence  of  plant  life  almost  everywhere  on  the 
earth  that  an  extreme  scarcity  of  plants  over  any  considerable 
area  seems  more  remarkable  than  does  their  abundance.  The 
complete  absence  of  living  plants  from  any  large  part  of  the 
land  surface  or  the  shallower  waters  is  a  condition  which  prob- 
ably seldom  occurs.  It  may  occur  in  regions  where  there  are 
poisonous  salt  deposits,  or  in  times  of  extreme  dryness,  or 
when  the  temperature  is  too  high  or  too  low  for  plants  to  live. 
Some  of  the  simplest  plants  can  for  long  periods  withstand  the 
most  intense  cold  ever  encountered  upon  the  earth,  and  a  few 
of  these  plants  can  withstand  high  temperatures  for  a  brief 
time.  Ordinarily  volcanoes  or  bodies  of  hot  lava,  and  some 
hot  springs  and  alkali  deposits  are  therefore  the  chief  visible 
portions  of  the  earth  which  are  quite  lifeless. 

It  is  a  matter  of  familiar  knowledge  that  the  lands  and  the 
waters  differ  greatly  in  the  density  of  their  plant  population. 
Some  areas  of  the  barest  Nebraska  sand  hills  do  not  on  the 
average  contain  more  than  one  flowering  plant  to  every  three 
thousand  square  feet,  while  a  weedy  garden  has  been  found 
to  contain  as  many  as  75,000  plants  in  a  similar  area.  If  the 
barest  portions  of  the  Sahara  were  compared  with  a  good  lawn 
or  meadow,  the  disproportion  would  be  far  greater.  The  purest 
natural  waters  contain  no  organisms  visible  to  the  eye,  while 
stagnant  pools  are  often  so  filled  with  pond  scums  and  other 
simple  and  minute  plants  that  each  cubic  inch  contains  many 

1 


2  PRACTICAL  BOTAXY 

thousands  of  individuals.  We  cannot  enumerate  all  the  kinds 
'of  /peaces',  'hi  ;whif,h  plants  find  lodgment  and  grow.  They 
occur  in  all  the  seas,  as  well  as  in  the  fresh  waters,  on  every 
kind  of  soil  from  the  wettest  swamps  to  arid  deserts,  on 
rocky  cliffs  and  the  bark  and  leaves  of  trees.  Microscopic 
forms  sometimes  occur  in  myriads  in  the  blood  of  animals, 
and  most  soils  teem  with  them  to  the  depth  of  several  inches 
below  the  surface. 

It  is  a  notable  fact  that  some  plants  are  the  smallest  and 
others  the  largest  of  living  beings,  and  it  is  evident  that 
plants  are  on  the  whole  by  far  the  most  conspicuous  of  living 
things. 

2.  Plants  and  animals.   A  little  thought  about  the  things 
upon   which   common    animals   feed   will   show   that   plants 
directly  or  indirectly  supply  food  for  animals.  Many  animals 
get  their  food  directly  from  living  plants,  in  the  form  of  roots, 
leaves,   seeds,  fruits,   etc.,   and  these    are    called   herbivores 
(plant  eaters).    Those  animals  called  carnivores,  which  eat 
the  flesh  of  other  animals,  are  dependent  upon  plants,  since 
their  prey  are  plant  feeders  or  may  live  upon  those  that  are 
plant  feeders.    In  one  way  or  another  all  animals  are  dependent 
upon  plants  for  food. 

3.  Plants  and  the  industries.   Man  is  also  directly  or  in- 
directly dependent  upon  plants  for  his  food.    His  animal  food 
is  indirectly  derived  from  plants,  his  bread  is  made  from  the 
seeds  of  plants,  and  there  is  a  constantly  growing  list  of  foods, 
spices,  and  flavors  that  are  prepared  from  roots,  stems,  leaves, 
seeds,  and  fruits. 

Much  of  the  work  in  which  men  are  engaged  is  performed 
by  domesticated  animals  as  beasts  of  burden,  or  is  concerned 
with  rearing  domesticated  animals  or  growing  plants  for  the 
market.  These  animals  could  not  be  cared  for  were  it  not  pos- 
sible to  feed  them  with  the  products  of  domesticated  plants, 
and  many  of  the  kinds  of  work  for  which  beasts  of  burden 
are  used  would  not  exist  were  it  not  for  the  need  of  growing 
plants  for  the  world's  uses. 


INTRODUCTORY  —  PLANTS  IN  NATURE  3 

The  domestication  and  improvement  of  plants  has  been  an 
essential  part  of  the  development  of  many  industries,  and  has 
advanced  until  at  the  present  time  the  greater  part  of  the 
food  of  the  world  is  secured  from  certain  kinds  of  plants 
which  once  grew  wild  and  produced  little  that  was  of  value 
to  men.  The  plant  producing  the  biggest  crop  in  the  world 
is  the  potato,  which  in  1906  produced  284,000,000,000  pounds 
of  potatoes.  But  the  most  important  crop  in  the  world  from 
the  point  of  view  of  the  market  value  of  its  product  is  wheat. 
In  each  of  three  great  agricultural  regions  of  the  United  States 
one  plant  is  dominant  in  its  value.  In  the  central  corn  belt 
there  are  seven  states  that  produce  nearly  one  half  the  corn 
used  in  the  whole  world,  an  amount  which  in  1909  was  worth 
nearly  $3,000,000,000.  The  Southern  States  produce  over 
three  fifths  of  the  cotton  of  the  world,  an  amount  worth 
nearly  $1,000,000,000.  The  Northwestern  States  produce 
wheat,  which,  while  not  so  large  a  proportion  of  the  world's 
crop,  is  of  tremendous  importance  to  the  welfare  of  the 
nation. 

Plant  fibers  are  extensively  used  in  the  manufacture  of 
clothing.  Timber  is  used  in  the  construction  of  buildings, 
furniture,  vehicles,  and  implements  for  use  in  the  industries. 
Plant  extracts  compose  the  most  of  our  medicines.  The  paper 
upon  which  our  ideas  are  recorded  is  made  chiefly  from  wood 
pulp,  though  it  is  now  proposed  to  make  it  from  cornstalks. 
The  processes  by  means  of  which  green  plants  live,  as  will  be 
shown  later,  contribute  to  the  purification  of  the  atmosphere 
that  we  breathe. 

The  farmers'  barns,  the  city  feed  stores,  warehouses,  cold- 
storage  establishments,  almost  every  manufactory  and  sales- 
room, and  many  of  the  railway  and  steamship  transportation 
lines  in  some  way  are  illustrations  of  the  important  relations 
which  plant  life  bears  to  the  fundamental  industries. 

4.  How  plants  live:  the  most  important  phase  of  botany. 
In  connection  with  the  preceding  discussion  regarding  the 
place  of  plants  in  nature,  it  must  be  clearly  understood  that 


4  PRACTICAL  BOTANY 

plant  structures  and  processes  are  of  importance  primarily  for 
their  function  in  maintaining  the  life  of  plants  themselves,  and 
that  their  use  in  the  industries  is  a  by-product  of  plant  life. 
The  body  of  a  tree  is  produced  in  the  tree's  ordinary  processes 
of  growth,  and  thereafter  it  chances  to  be  useful  to  men  for 
timber.  Though  corn  and  wheat  have  been  improved  artifi- 
cially until  now  they  supply  much  of  the  food  of  mankind,  in 
nature  as  wild  plants  they  produced  seeds  which  were  small 
but  sufficed  to  give  rise  to  new  plants.  The  possibilities  of 
utility  result  from  the  ordinary  activities  and  structures  of 
plants,  and  the  study  of  these  possibilities  must  be  made 
accessory  to  the  consideration  of  the  general  principles  of 
plant  life.  What  plants  are  and  how  and  where  they  live  are 
the  most  fundamental  questions,  and  are  the  ones  which  we 
shall  first  consider  in  the  following  chapters. 


CHAPTER  II 


GENERAL  STRUCTURE  AND  WORK  OF  PLANTS l 

5.  Introductory.    Any  one  of  our  most  familiar  plants  con- 
sists  of  roots,   stem,   leaves,   flowers,   and  fruits   containing 
seeds.    Each  of  these  parts  is  usually  distinct  (Fig.  1).    Each 
does  one  or  more  particular  kinds 

of  work,  and  together  they  do 
the  work  of  the  whole  plant. 
The  plant,  therefore,  is  a  complex 
structure,  whose  life  is  depend- 
ent upon  the  work  of  its  different 
parts. 

6.  Roots  and  their  work:  anchor- 
age.   The  most  obvious  work  of 
roots   is  done  in   holding  plants 
in  place,  or  in  giving  them  an- 
chorage.    On  steep   hillsides,  on 
banks   of    streams,   and   in   shal- 
low  soil   which  lies  upon  stone, 
the  amount  of  anchorage  which 
roots    afford    is    often    so    small 


FIG.  1.   A  buttercup  (Ranun- 
culus acris) 


The  plant  consists  of  roots,  stem, 
leaves,  flowers,  and  seeds.  A,  the 
plant,  shown  about  one  eighth  natu- 
ral size ;  B,  cluster  of  ripened  seeds, 
shown  almost  natural  size;  (7,  a 
section  through  one  seed,  shown 
almost  three  times  natural  size 


1  This  chapter  presents  an  outline  of  a 
plant  as  a  working  machine.  It  does  not 
include  details  but  gives  a  general  view 
of  the  plant  and  the  kind  of  work  that  it 
does.  If  this  outline  chapter  is  studied 
briefly,  later  discussions  will  be  more 

easily  understood  and  more  profitable  than  if  numerous  details  are  pre- 
sented first.  The  chapter  should  be  read  carefully  by  each  member  of 
the  class  and  discussed  in  one  or  two  recitations,  or  it  may  be  read  and 
discussed  by  pupils  and  teacher  together. 


6  PRACTICAL  BOTANY 

that  trees  are  uprooted  (Fig.  4)  in  times  of  heavy  wind.  In 
other  cases  the  anchorage  may  be  so  great  that  during  a  heavy 
wind  the  plant  will  be  broken  off  instead  of  having  its  roots 
upturned.  A  study  of  such  situations  as  those  just  mentioned 
will  give  some  idea  of  the  distance  to  which  the  larger  roots 
spread  and  of  the  amount  of  soil  that  lies  as  weight  upon  them. 


A 

FIG.  2.  Tips  of  two  cornstalks 

A  is  in  normal  growing  condition,  while  B,  through  excessive  loss  of  water,  has 
wilted  and  its  leaves  are  contracted  into  tube-like  rolls 

7.  Roots  and  their  work:  water  supply.  Water  is  essential 
to  the  growth  of  plants.    Plants  of  the  farm,  garden,  lawn, 
and  those  commonly  grown  in  our  homes  have  their  roots  in  the 
soil  and  their  stems  and  leaves  in  the  air,  and  therefore,  if  they 
secure  water  at  all,  must  get  it  from  the  soil  or  air,  or  both. 
When  roots  are  deprived  of  water  the  plants  soon  wilt  (Fig.  2) 
and  eventually  die.    If  one  should  pour  water  upon  the  stems 
and  leaves,  but  deprive  the  roots  of  it,  the  plants  would  not 
thrive.    Ordinarily  roots  secure  water  for  the  entire  plant. 

8.  Roots  and  their  work:  root  hairs.  Most  root  systems  branch 
near  the  base  of  the  stem  and  continue  to  subdivide  (Fig.  3) 


FIG.  3.  The  root  system  of  the  corn  plant 

The  soil  has  been  washed  away  so  as  to  show  the  quantity  and  spread  of  the  roots, 

and,  to  some  extent,  the  positions  that  they  assume  in  the  soil.  Photograph  by  the 

United  States  Department  of  Agriculture 


FIG.  4.  Two  upturned  spruce  trees  which  grew  upon  a  stony  surface 

The  entire  root  system  spread  over  the  rock  did  not  provide  sufficient  anchorage 
to  hold  the  tree  in  place  in  time  of  a  very  heavy  wind 

7 


8 


PRACTICAL  BOTANY 


until  the  roots  are  extremely  small.  During  periods  of  active 
growth  root  hairs  appear  upon  the  smaller  rootlets  (Fig.  5). 
These  rootlets,  like  the  other  parts  of 
the  plant,  are  made  up  of  many  cells 
(Fig.  6).  Each  cell  has  a  wall,  the  cell 
wall,  which  incloses  the  living  mate- 
rial, called  the  protoplasm.  In  the 
root  hairs,  as  in  Fig.  6,  two  parts  of 
the  protoplasm  are  shown,  the  nucleus 
and  the  granular  cytoplasm.  Cells  con- 
tain other  protoplasmic  bodies,  which 
need  not  be  discussed  at  this  time. 
The  root  hairs  are  extensions  of 
the  surface  or  epidermal  cells  of  the 
rootlet  and  are  parts  of  those  cells. 
They  grow  a  little  way  back  from 
the  tip  of  the  rootlet  and  new  ones 
appear  as  the  root  tip  pushes  for 
ward  in  the  soil,  so  that  with  the 
dying  of  older  root  hairs  and  the  de-  Note  the  diff  erence  in  length  and 

velopment  of  newer      condition  of  the  root  hairs  on  the 

ones  on  new  growth         different  parts  of  the  root 
of  the  rootlet,  the  actual  number  of  root  hairs 
n  on  a  rootlet   during 

the  growing  season 
may  remain  practi- 
cally constant.  It  is 
evident  that  the  area 
of  root  hairs  on  a 
rootlet  advances,  al- 
though  the  single  root 
hairs  do  not  move  f  OI'- 


FIG.  5.    A  mustard  seedling 

grown  in  a  band  of  filter  paper 

inside  a  drinking  glass  so  as  to 

show  the  root  hairs 


w 


FIG.  6.  Cells  from  the  surface  of  a  young  rootlet 
Showing  epidermal  cells  (e),  and  one  young  and  two 
older  root  hairs  (A).  In  the  root  hairs  the  nucleus 
(n)  and  granular  cytoplasm  of  the  cells  are  shown. 

Greatly  magnified 

laterally  from  the  rootlet,  growing  through  the  soft  particles 
of  the  soil  and  around  the  harder  ones,  thus  constituting  a 


The  root  hairs  extend 


STRUCTURE  AND  WORK  OF  PLANTS  9 

network  in  the  region  about  the  tip  of  the  rootlet.  If  the 
seedlings  are  grown  in  sawdust,  on  damp  blotting  paper,  or 
within  earthen  pots  that  are  kept  moist  by  covering  or  by 
being  inverted  upon  a  damp  surface,  they  will  afford  interest- 
ing demonstrations  of  how  rootlets  and  root  hairs  grow  under 
different  conditions. 

9.  Roots  and  their  work :  water-lifting  power.   If  the  top 
of  a  vigorously  growing  potted  plant  is  cut  off  and  an  upright 
glass  tube  is  attached  to  the  plant  stump  by  means  of  a  rubber 
tube,  water  may  be  forced  upward  in  the  latter,  thus  showing 
that  roots  can  lift  water  from  the  soil.  Actively  growing  trees 
and  shrubs,  when  cut,  often  show  this  same  phenomenon  by 
forcing  out  through  the  cut  surface  some  of  the  water  that 
is  brought  up  from  the  soil.    This  is  sometimes  incorrectly 
spoken  of  as  "  bleeding  "  of  the  stump.    The  roots,  however, 
are  not  the  only  parts  of  the  plant  that  may  lift  water.    That 
the  leaves  and  stem  may  also  do  this  work  may  be  shown  by 
cutting  off  the  top  of  a  plant  under  water,  and,  while  still  under 
water,  attaching  the  stem  to  a  water-filled  U-shaped  tube.    The 
top  of  a  plant  that  has  been  so  treated  may  continue  to  lift 
water  for  several  days. 

In  plants  that  are  growing  normally,  the  roots,  by  means  of 
the  root  hairs,  take  up  water  from  the  soil.  It  passes  into  the 
interior  of  the  rootlet,  then  into  the  larger  roots,  into  the  stem, 
and  finally  into  the  leaves.  Some  of  this  water  is  carried  from 
the  leaves  into  the  air,  and  that  process  will  be  discussed  under 
the  topic  transpiration. 

10.  Roots  and  their  work :  turgidity.  Root  hairs  and  other 
cells  of  plants  usually  take  up  water  until  the  cell  walls  are 
distended  with  water  and  protoplasm.    The  outward  pressure 
which  distends  and  stretches  the  walls  is  called  turgor,  and  the 
resulting  condition  is  called  turgidity.    Turgor  doubtless  helps 
to  force  water  upward  through  the  stem.    The  distention  of 
cells  due  to  turgor  also  accounts  for  the  rigid  or  erect  position 
of  most  leaves,  growing  shoots,  and  succulent  stems.    Each 
distended  cell,  like  an  inflated  balloon,  assumes  a  semi-rigid 


10 


PRACTICAL  BOTANY 


position,  and  a  mass  of  distended  cells  pressing  against  one 
another  makes  the  whole  structure  rigid.  But  as  when  the  air 


FIG.  7.  A  photograph  of  a  cottonwood  leaf  from  which  the  green  tissue  has 

been  removed  so  as  to  show  the  network  of  veins  through  which  the  food 

material  is  carried  throughout  the  leaf  and  to  the  stem 

Natural  size.   Leaf  prepared  by  Ellsworth  Bethel 

escapes  from  a  balloon  its  wall  collapses  of  its  own  weight, 
so  do  the  cells  of  the  leaves  and  shoots  when,  through  loss 
of  water,  they  lose  their  turgidity.  When  soil  water  is  not 


STRUCTURE  AND  WORK  OF  PLANTS  11 

available  to  the  plant,  the  outgo  from  the  leaves  is  often 
greater  than  .the  income  from  the  roots,  and  in  such  cases 
wilting  follows.  If  water  does  not  again  become  available, 
the  plant  will  die,  but  with  a  renewed  supply  turgidity  and 
the  resulting  rigidity  soon  return. 

11.  Stems  and  their  work:  water  passes  through  the  stem. 
The  stem  is  a  means  of  connection  between  the  roots  and  the 
leaves.  It  also  serves  to  support  the  leaves  in  the  air.  Ascend- 
ing water  passes  mainly  through  special  regions  of  the  stem 
and  the  leaf.    When  a  fresh  leaf  of  celery  or  leafy  stem  of 
hydrangea  is  placed  for  a  few  minutes  in  one  of  the  ani- 
line dyes,  and  then  removed  and  examined  by  sectioning,  defi- 
nitely stained  regions  appear,  which  show  not  only  that  the 
staining  liquid  passed  upward  into  the  stalk,  but  that  it  passed 
through  only  certain  tissues  of  the  stalk.    These  special  tissues 
through  which  the  liquids  pass  are  composed  of  bundles  of 
very  small  tubular  cells  which  are  many  times  as  long  as  they 
are  thick.    The  bundles  are  known  as  fibrovascular  bundles, 

—  which  term  simply  means  "  collections  of  thread-like  tubes." 
The  different  cells  of  these  bundles  overlap  one  another  in 
such  a  way  that  they  are  continuous  from  roots,  through  stem 
and  branches,  into  the  leaves.  In  the  leaves  the  bundles  are 
the  so-called  veins 
(Fig-  7). 

12.  Stems  and 
their  work:  kinds 
of  stems.  There  is 
a  striking  and  im- 
portant difference 
in    the    arrange- 
ment of  fibrovas-     FIG.  8-  A  cornstalk  broken  so  as  to  show  the  number 

la     b      die     '  anc*  ^istribution  of  tlie  vascular  bundles 

the  stems  of  different  kinds  of  plants.  If  a  stem  of  corn  or  a 
plantain  leafstalk  is  broken,  whitish  strings  are  pulled  from 
the  pith  (Fig.  8).  These  are  vascular  bundles.  They  are 
somewhat  irregularly  distributed  throughout  the  stem,  and 


12 


PKACTICAL  BOTANY 


-,-6 


'-P 


FIG.  9.  Diagram  of  a  cross  section  of 
a  geranium  stem 

The  regions  are  the  outer  bark  (6) ,  the 

cortex  (c),  the  woody  tissue  (w),  and  the 

pith  (p) 


are  intermingled  with  the  soft  pith  tissue.  There  is  a  large 
group  of  plants,  the  monocotyledons,  which  have  the  irregular 
distribution  of  bundles  just  described.  In  such  stems  there  is 

usually,  around  the  outside,  a 
much  harder  tissue,  which  is 
extremely  strong,  and  which 
..c  serves  to  strengthen  the  stem. 
In  other  kinds  of  plants  a 
cylinder  of  bundles  is  defi- 
nitely arranged  about  the  pith 
(Fig.  9),  and  this  arrangement 
is  also  characteristic  of  a  great 
group,  the  dicotyledons.  Other 
features  of  these  groups  are 
discussed  in  later  chapters, 
and  in  this  connection  it  is 
important  only  to  note  some 
general  characters  of  the  stem. 
13.  Stems  and  their  work :  annual  growth.  In  many  of  our 
common  annual  plants  (those  that  live  for  but  one  year)  the 
arrangement  of  the  bundles  or  woody  tissue  in  the  form  of  a 
cylinder  about  the  pith  is  readily  seen.  In  such  plants  the  pitli 
usually  occupies  more  of  the  stem  than  does  the  wood.  The 
proportion  of  pith  to  wood  is  much  less  in  the  perennial  plants 
(those  that  live  for  two  or  more  years).  In  a  cross  section  of 
one  of  the  common  trees,  unless  the  specimen  be  quite  young, 
it  will  be  difficult  or  impossible  to  discover  any  pith  region. 
The  greater  part  of  the  section  is  made  up  of  wood.  Each 
year  there  is  formed  a  layer  of  this  woody  tissue  from  the 
inner,  heavy-walled  cells  of  the  bundles,  which  persist  and 
give  strength  and  support  to  the  whole  tree.  The  great  size 
of  our  forest  trees  is  made  possible  by  this  arrangement  of 
bundle  tissues.  The  record  of  growth  may  be  .read  by  stud};  - 
ing  the  rings  of  wood.  The  amount  of  a  year's  growth  and 
the  total  time  that  a  tree  has  lived  can  be  reckoned.  You  will 
also  find  it  interesting  to  study  the  top  of  your  desk  or  th« 


STEUCTUEE  AND  WOEK  OF  PLANTS 


13 


furniture  in  the  room  to  see  if  you  can  recognize  the  partial 
rings  of  wood  or  can  tell  the  way  in  which  the  timber  was 
sawed.  In  later  chapters  there  will  be  a  more  extensive  study 
of  stems  and  the  ways  in  which  they  grow. 

14.  Leaves,  general  form  :  the  epidermis.  Most  leaves  con- 
sist of  two  parts,  —  the  leafstalk  or  the  petiole,  and  the  blade, 
which  is  the  expanded  portion.  In  some  leaves  the  petiole 
is  absent,  and  in  others  the  blade  is  subdivided  into  several 
parts,  in  which  case  the  leaf  is  said  to  be  compound.  To  most 
observers  leaves  appear  to  be  a  uniformly  green  mass  of  mate- 
rial. More  careful  observation  discloses  the  fact  that  many 
leaves  are  not  .equally  green  on  both  surfaces,  and  that 
running  throughout  the  leaf  there  are  more  or  less  regularly 
arranged  veins  or  fibrovas- 
cular  bundles  which  are  not 
green. 

From  the  upper  and  lower 
surfaces  of  leaves  such  as 
those  of  live-forever,  Wan- 
dering Jew,  Easter  lily,  and 
epiderwort  one  may  peel  a 
thin,  almost  colorless  layer, 
which  is  known  as  the  epider- 
mis (Fig.  10).  The  epidermis 
is  composed  of  cells  more  or 
less  compactly  arranged.  In 
the  epidermis  from  one  and 
sometimes  from  both  sur- 
faces there  are  special  struc- 
tures known  as  stomata 
(Fig.  10).  From  a  surface 
view  a  stoma (plural,  stomata) 
presents  two  more  or  less  crescentic  or  kidney-shaped  cells, 
the  guard  cells,  between  which  is  an  elliptical  opening,  the 
stomatal  opening.  Unlike  other  epidermal  cells,  the  guard  cells 
are  greenish.  The  opening  serves  as  a  place  of  entrance  for 


FIG.  10.  A  surface  view  of  leaf  epider- 
mis from  the  geranium  (Pelargonium) 

Among  the  ordinary  epidermal  cells  (c)  are 
four  stomata,  each  with  two  guard  cells  (gc) 
and  the  mouth  of  an  air  cavity  (p).   Con- 
siderably magnified 


14 


PRACTICAL  BOTANY 


most  of  the  carbon  dioxide  used  by  the  plant.  The  guard 
cells  press  closely  together,  or  they  may  separate  until  a  cir- 
cular opening  is  formed,  and  in  thus  closing  and  opening  they 
influence  the  interchange  of  air  between  the  interior  and  the 
exterior  of  the  leaf.  This  obviously  affects  the  interchange  of 
such  gases  as  carbon  dioxide  and  oxygen,  as  well  as  the  outgo 
of  moisture  from  the  leaf. 

15.  Leaves :  internal  structure.    The  interior  cells  of  the 
leaf,  except  those  of  the  veins,  are  colored  green  by  chlorophyll, 


FIG.  11.  Cross  section  of  a  geranium  leaf 

a,  air  space;  a.c,  air  chamber;  e,  upper  epidermis;  e',  lower  epidermis;  p,  pali- 
sade cells;   s,  stoma;  sp,  spongy  parenchyma  (usually  spongy  parenchyma  has 
fewer  chloroplasts  than  the  palisade  tissue) ;  v,  vein.  Magnified  150  times.   After 
drawing  by  Mrs.  F.  E.  Clements 

which  means  "  leaf  green."  The  cells  are  not  uniformly  green, 
but  the  chlorophyll  is  contained  in  special  small  bodies, 
known  as  chloroplasts  or  chlorophyll  bodies  (Fig.  11),  which 
are  within  the  cells.  It  must  be  clearly  understood  that  the 
chloroplast  and  the  chlorophyll  are  not  the  same.  Plastids 
(plasts)  may  or  may  not  contain  chlorophyll,  just  as  a  sponge 
may  or  may  not  contain  water.  It  is  evident,  therefore,  that 
a  plastid  can  properly  be  called  a  chloroplast  only  when  it 
contains  chlorophyll. 


STRUCTURE  AND  WORK  OF  PLANTS  15 

In  summing  up  the  structures  of  the  leaf  we  may  say  that 
it  usually  consists  of  a  petiole  and  a  blade.  The  outer  portions 
of  the  blade  both  above  and  below  are  the  epidermis ;  in  ad- 
dition to  the  ordinary  epidermal  cells  the  epidermis  contains 
special  structures,  —  the  stomata  ;  within  the  epidermis  are  the 
veins  and  masses  of  green  tissue ;  the  green  tissues  are  made 
up  of  more  or  less  compact  cells  in  which,  in  addition  to  other 
cell  contents,  are  plastids,  which  contain  the  green  coloring 
matter,  chlorophyll. 

16.  Leaves:  material  for  leaf  work.  In  connection  with  the 
discussion  of  roots  and  stems  it  was  found  that  water  is  carried 
into  the  leaves.    In  the  soil  are  many  substances  which  are 
dissolved  by  the  water,  just  as  common  salt  or  sugar  would 
be.  When  water  is  taken  up  into  the  plant  some  of  these  sub- 
stances that  are  in  solution  also  enter.    In  this  way  there  may 
be  carried  into  the  plant  compounds  containing  such  things  as 
nitrogen,  potassium,  phosphorus,  sulphur,  and  iron.    Through 
the  surface  of  the  leaf,  chiefly  through  the  stomata,  the  plant 
secures  carbon  dioxide.    This  is  a  gaseous  substance  which 
exists  in  the  atmosphere  in  the  ratio  of  about  .3  parts  in  10,000 
of  air.    Inside  the  leaf,  therefore,  there  is  a  supply  of  the  so- 
called  raw  materials  for  food,  —  as  water,  carbon  dioxide,  and 
substances  that  were  in  solution  in  soil  water. 

17.  Leaves:  food  manufacture.   Carbon  dioxide  and  water 
must  undergo  change  before  they  can  be  used  in  nourishing  and 
building  up  the  plant.    The  sun  shines  upon  the  leaf  and  the 
chlorophyll  absorbs  some  of  the  energy  from  the  sun's  rays. 
This  energy  serves  in  some  way  as  yet  unknown  to  break 
up  the  compounds  water  and  carbon  dioxide  into  the  carbon, 
hydrogen,  and  oxygen  of  which  they  are  made.    The  carbon, 
hydrogen,  and  some  of  the  oxygen  immediately  unite  again ; 
not,  however,  into  the  compounds  carbon  dioxide  and  water, 
but  into  new  compounds.   These  rapidly  pass  through  several 
changes  and  may  finally  become  sugar  and  starch.   At  present 
the  changes  before  starch  and  sugar  are  formed  are  not  all 
known.   Some  of  the  oxygen  resulting  from  the  breaking  up 


16  PKACTICAL  BOTANY 

of  carbon  dioxide  and  water  is  used  in  making  starch  and 
sugar,  but  much  of  it  is  set  free  and  may  pass  out  into  the  air. 
The  oxygen  thus  set  free  by  plants  may  be  collected  as  shown 
in  Fig.  12  and  then  tested.  This  process  that  is  carried  on  by 
green  plants  is  a  principal  factor  in  maintaining  the  oxygen 
supply  that  is  so  necessary  to  the  life  of  animals.  Plants  also 
use  some  free  oxygen  in  some  of  their  later  food-making  proc- 
esses. This  series  of  occurrences  by  means  of  which  green 
plants  under  the  influence  of  sunlight  make  foods,  such  as 
starch  and  sugar,  from  carbon  dioxide  and  water,  is  known 
as  photosynthesis.  The  word  photosynthesis  means  "  putting 
together  by  means  of  light."  1 

1  The  chemistry  of  photosynthesis  is  not  completely  known,  but  some  of 
the  simpler  aspects  of  it  may  prove  valuable  at  this  point.  Water  is  usually 
expressed  by  the  chemist  by  the  formula  H2O,  in  which  H  stands  for  hydro- 
gen and  O  for  oxygen,  and  the  figure  2  indicates  that  two  parts  of  hydrogen 
are  united  with  one  part  of  oxygen.  Similarly  CO2  indicates  that  one  pait 
of  carbon  is  united  with  two  parts  of  oxygen  to  form  carbon  dioxide.  When 
these  compounds  are  broken  up,  there  is,  for  a  very  brief  time  at  least1,, 
free  C,  H,  and  O.  If  one  unit  of  each  compound  (H20  and  CO2)  is  thus 
broken  up,  there  will  be  two  H,  one  0,  one  C,  and  two  0  (or  in  all  three  0). 
After  photosynthesis  has  been  going  on  for  some  time,  starch  is  usually 
formed.  Starch  consists  of  (C6H10O5)  "n".  This  means  that  six  parts  of 
carbon,  ten  parts  of  hydrogen,  and  five  parts  of  oxygen  unite  to  form  stare 
and  the  ftn"  means  that  the  unit  C6H10O5  does  not  appear  singly,  but  that 
an  unknown  number  of  them  are  united.  Disregarding  the  fact  that  sev- 
eral of  the  starch  units  are  held  together,  and  considering  the  single  unit 
C6H10O5,  we  may  be  able  to  see  what  happens  in  the  work  of  photosynthesis. 
To  secure  the  amount  of  carbon  necessary  to  form  starch,  six  times  the  unit 
CO2  must  be  taken,  since  there  are  to  be  used  six  units  of  carbon.  To  secure 
the  needed  amount  of  hydrogen,  five  times  the  unit  H20  must  be  used, 
since  there  must  be  ten  units  of  hydrogen  and  two  are  secured  with  each 
unit  of  water.  We  have,  therefore,  6  C02  and  5H2O.  When  the  energy 
of  the  sun  has  broken  these  things  into  their  constituent  parts  there  are 
6C,  12  O,  10  H,  and  5O,  or  17  O  in  all.  But  starch  consists  of  C6H1005, 
and  in  making  this  unit  of  starch  there  has  been  used  all  of  the  carbon, 
all  of  the  hydrogen,  and  five  units  of  the  oxygen,  thus  leaving  twelve 
units  of  oxygen  to  be  set  free  or  to  be  used  by  the  plant  in  some  other 
way.  Some  of  this  free  oxygen  passes  into  the  air,  though  some  of  it  is  used 
by  the  plant  in  a  later  process. 

The  compounds  thus  constructed,  as  starch  and  sugar,  are  called  carbo- 
hydrates, the  name  indicating  that  they  are  compounds  of  carbon  and 
water. 


STEUCTUEE  AND  WOEK  OF  PLANTS 


17 


Sugar  and  starch  may  be  used  as  food  by  the  plant,  being 
transported  to  and  made  into  the  living  parts  of  the  plant. 
Or  these  things  may  be  made  [^ 
into  more  complex  foods,  (Vpt 
known  as  the  proteins,  by  Irhf 
the  addition  of  some  of  the 
compounds  of  nitrogen,  potassium, 
phosphorus,  or  other  substances, 
and  then  digested  and  used  by  the 
plant.  Replenishment  and  growth 
of  new  parts  can  take  place  only 
by  means  of  foods,  and  since  the 
plant  makes  its  own  supply,  the 
importance  of  the  process  is  very 
great. 

Manufactured  foods  are  carried 
to  all  the  living  parts  of  the  plant. 
They  may  also  be  stored  in  almost 
any  plant  structure.  When  in  proc- 
ess of  moving  through  the  plant, 
these  foods  are  believed  to  pass 
through  the  soft  portions  of  the 
fibrovascular  bundles. 

Furthermore,  often  more  food  is 
made  by  green  plants  than  they  FIG.  12.  Apparatus  for  collect- 
need  at  the  time,  or  even,  in  case  ing  oxygen  from  working  plants 
of  some  plants,  than  they  ever  use,  "SSSSSSlSSffSt 

and  this  is    Stored  most    Commonly      uate.    Bubbles  of  oxygen  pass 

in  the  form  of  starch,  though  some-     uPward  f5Qm  thf  cu* ends  of  fe 

&  stems  and  crowd  out  some  water 

times    in    Other  forms.     This    Stored  from  the  previously  filled  grad- 

food    may    be     USed     later    by    the  uate.  The  ordinary  test  for  oxy- 

J  J  gen  with  a  burning  stick  will 

plant,  Or  as  food  for  men  and  Other  determine  whether  it  is  present. 

animals.     It  may  also  be  moved  by  In  such  an  experiment  care  must 

_ .  *        •  ,  J  be  taken  to  see  that  there  is 

the  plant  and  stored  in  a  different     plenty  of  space  about  the  collect- 
structure  from  that  in  which  it  was    ins tube  to5f™it  *re*  passfge 

of  the  gases  that  are  m  the  water, 
first  located.  After  Ganong 


18  PRACTICAL  BOTANY 

18.  The  work  of  the  leaf :  transpiration.  When  a  potted 
plant,  so  covered  that  no  moisture  can  escape  from  the  pot 
or  earth,  is  placed  under  a  dry  bell  jar,  within  a  few  hours 
moisture  is  seen  to  collect  upon  the  inner  surface  of  the  jar. 
After  a  longer  time  the  amount  of  moisture  may  cause 
streams  or  large  drops  of  water  to  run  down  the  inner  wall 
of  the  jar. 

If  a  plant  that  wi]l  thrive  with  its  roots  in  water  is  planted 
in  a  jar  of  water  and  carefully  sealed  around  the  stem,  and 
the  whole  apparatus  weighed  from  day  to  day,  a  constant  loss 
of  water  may  be  demonstrated.  Water  is  ordinarily  taken  up 
by  the  plant  in  much  larger  quantities  than  are  used  for  the 
work  of  photosynthesis.  Large  amounts  of  water  are  carried 
into  the  air  through  the  leaves.  By  making  careful  demon- 
strations of  the  weight  and  volume  of  this  water  loss  and  the 
area  of  the  leaf  surface  that  is  exposed,  it  is  possible  to  deter- 
mine the  'amount  of  water  which,  on  an  average,  passes  through 
each  square  inch  of  leaf  surface  in  a  given  time.  This  evapo- 
ration or  loss  of  water  from  the  plant  is  known  as  transpira- 
tion, and  the  current  of  water  thus  passing  through  the  plant 
is  called  the  transpiration  current.  Water  evaporates  from  the 
stomatal  openings  or  from  other  parts  of  the  leaf  surface.  As 
superficial  evaporation  occurs,  water  from  the  moister  portions 
of  the  plant  must  take  the  place  of  that  evaporated,  or  there 
is  danger  of  injury  to  the  plant.  Such  danger  and  resulting 
death  often  occur,  due  to  great  or  sudden  loss  of  water. 

The  quantity  of  water  loss  in  transpiration  is  often  surpris- 
ingly great.  It  has  been  estimated  in  one  case  that  a  beech  tree 
110  years  old,  in  one  summer  transpired  approximately  2250 
gallons  of  water ;  that  an  oak  tree  with  700,000  leaves  tran- 
spired about  180  gallons  of  water  daily ;  and  that  an  acre  of 
cabbages  in  their  growing  season  (about  four  months)  tran- 
spired 500,000  gallons  of  water.  One  can  scarcely  picture  in 
his  mind  the  immense  quantity  of  water  that  is  constantly 
transpiring  from  all  the  vast  stretches  of  forests,  grasslands, 
farm  crops,  roadside  weeds,  and  swamp  plants. 


STRUCTURE  AND  WORK  OF  PLANTS  19 

19.  The  work  of  the  leaf :  temporary  responses.    On  exces- 
sively dry  days  plants  such  as  wheat  and  com  sometimes 
wilt,  since  they   are  transpiring  more  water  than  they  are 
securing.    If  the  soil  becomes  very  hard,  the  water  passes 
into  the  air  quite  readily ;  but  if  the  soil  is  kept  well  pulver- 
ized upon  the  surface,  more  soil  water  is  held  and  a  larger 
supply  is  available.    Observations  made  upon  a  garden  that 
is  constantly  cultivated  during  hot,  dry  weather,  and  upon 
one  that  is  not  so  cultivated,  show  a  great  difference  in  ability 
of  the  plants  to  withstand  drought.    In  a  cornfield  on  a  dry, 
hot  day  the  leaves  of  the  corn  often  roll  into  rather  tight 
tubes.    This  form  of  leaf  exposes  less  surface  to  evaporation 
and  consequently  loses  less  water  than  would  the  fully  ex- 
panded leaves.    This  habit  is  doubtless  of  advantage  in  main- 
taining a  balance  in  water  supply. 

In  setting  out  young  orchard  or  shade  trees,  nurserymen 
recommend  that  the  branches  be  well  pruned ;  otherwise  the 
leaves  may  soon  grow  in  such  numbers  that  they  will  tran- 
spire more  water  than  comes  into  the  newly  transplanted 
trees,  which  do  not  have  their  ordinary  amount  of  absorbing 
root  surface.  Obviously  newly  transplanted  trees  and  garden 
plants  should  be  kept  especially  well  watered  until  their  root 
systems  are  well  formed. 

20.  Respiration.    The  work  of  respiration    in   both  plants 
and  animals  is  commonly  associated  with  the  interchange  of 
gases  between  the  exterior  and  interior  of  the  living  body.  In 
plants  the  interchange  of  gases  may  take  place  through  the 
leaf  or  through  other  parts  of  the  plant.    This  interchange, 
however,  is  no  longer  regarded  as  the '  fundamental  thing  in 
respiration,  since  respiration  takes  place  in  active,  living  pro- 
toplasm in  all  parts  of  the  plant.    It  consists  in  decomposition 
of  protoplasm  or  of  some  of  its  parts,  or,  as  is  supposed  by 
some  physiologists,  it  may  consist  in  decomposition  of  food 
materials  that  have  not   yet   become   protoplasm.    Through 
respiration  complex  plant  substances  are  broken  down,  and 
the  energy  released  by  this  decomposition  is  the  energy  by 


20 


PRACTICAL  BOTANY 


means  of  which  plants  carry  on  their  work.  Energy  in  the 
form  of  heat  is  also  one  of  the  results  of  respiration.  Respira- 
tion may  occur  in  the  absence  of  free  oxygen,  but  is  more 
complete,  and  thus  releases  more  energy,  when  oxygen  is 
present.  When  respiration  is  complete,  it  results  in  the  forma- 
tion of  various  compounds,  chief  of  which  are  carbon  dioxide 
and  water.  Carbon  dioxide  and  water  may  be  carried  from  the 
plant  through  the  leaf,  or  other  parts  of  the  plant,  and  the 
oxygen  supply  may  enter  in  the  same  way.  It  is  evident,  how- 
ever, that  the  transfer  of  these  gases  is  an  incident  associ- 
ated with  the  real  respiration,  which  consists  in  decomposition 
of  complex  substances  and  the  release  of  energy  therefrom. 
Also  it  is  evident  that,  so  far  as  respiration  is  concerned,  plants 
and  animals  behave  in  the  same  way.  It  should  be  noted  that 
in  photosynthesis  green  plants  utilize  carbon  dioxide,  though 
they,  like  other  plants  and  animals,  may  produce  carbon  dioxide 
as  one  of  the  products  of  respiration. 

21.  Flowers  and  seeds  :  the  parts  of  the  flower.    The  flower 
is  the  part  of  the  plant  by  means  of  which  seeds  are  produced. 

Flowers   differ 

^Corolla      ^W\  widely,  but  an 

examination  of 
any  such  sim- 
ple flower  as 
that  of  the  gera- 
nium or  the  ox- 
alis  shows  that 
there  are  four 
kinds  of  floral 
parts  in  it  (Fig. 
FIG.  13.  Drawings  of  two  flowers  13).Outermost 

A,  entire  flower  ;  B,  part  of  the  floral  structures  removed  -j  iowpsf  j«  a 

set  of  greenish  leaves  known  collectively  as  the  calyx,  the  sep- 
arate leaves  being  known  as  the  sepals.  Just  above  the  calyx, 
and  usually  larger  and  more  conspicuous,  is  the  corolla,  each 
leaf  of  which  is  a  petal.  Above  the  corolla  is  the  group  of 


STRUCTURE  AND  WORK  OF  PLANTS 


21 


stamens,  easily  recognized  by  their  slender  stalks  and  the  en- 
larged tips  which  are  known  as  the  anthers.  Within  the  anther 
is  the  pollen  or  pollen  grains.  At  the  tip  of  the  flower,  within 
the  group  of  stamens,  is  the  pis- 
til, consisting  of  one  or  more 
units  or  carpels.  Often  the  tip  of 
the  pistil  is  expanded,  and  some- 
times divided  into  two  or  more 
short  branches,  this  portion  being 
called  the  stigma;  the  elongated 
part  of  the  pistil  is  the  style,  and 
the  swollen  base  is  the  ovary, 
so  called  because  it  contains  the 
ovule  or  ovules.  The  ovules  are 
the  developing  seeds. 

22.  Flowers  and  seeds:  seed 
formation.  The  ovules  begin  their 
development  within  the  ovary, 
but  cannot  alone  form  mature 
seeds  which  will  grow  into  new 
plants.  Some  of  the  .pollen  from 
the  anther  of  the  same  or  an- 
other flower  falls  upon  the  stigma 
(Figs.  13, 14,  and  15).  From  one 
or  more  of  these  pollen  grains 
there  grows  down  through  the 
style  into  the  ovule  an  extremely 
small  tube.  Inside  this  tube  are 
carried  some  of  the  cellular  con- 
tents of  the  pollen  grain,  which 
meantime  have  divided  into  three 
cells.  One  of  these  cells  thus 
carried  into  the  ovule  by  the  pollen  tube  unites  with  a  special 
egg  cell  that  is  formed  within  the  ovule  (Fig.  14).  The  cell 
that  is  made  by  the  union  of  the  one  from  the  ovule  and  the 
one  from  the  pollen  tube  grows  into  the  new  plant  within 


FIG.  14.  A  diagram  of  a  pistil 
(carpel) 

Within  the  cavity  of  the  ovary  is  an 
ovule  (n),  and  within  the  ovule  is 
an  embryo  sac.  At  the  free  end  of 
the  ovule  is  the  micropyle  (ra).  In 
the  end  of  the  embryo  sac  near  the 
micropyle  is  the  egg  (egg)  with  two 
other  nuclei  lying  close  to  it ;  in  the 
center  of  the  sac  is  the  endosperm 
nucleus  (en) ;  and  at  the  other  end 
are  the  antipodal  nuclei  (a) .  Pollen 
grains  (p)  are  on  the  stigma,  and 
from  one  is  shown  a  pollen  tube 
which  has  grown  down  to  the  egg 


A 


B 


FIG.  15.  Stages  in  the  development 
of  the  bean  pod 

A,  pistil  of  a  bean  flower,  showing  the 
ovary  (o),  style  (sty),  and  stigma  (sti) ; 
also  the  calyx  at  the  base  of  the  pistil. 

B,  a  pistil  a  few  days  older,  in  which 
the  ovary  has  grown,  and  from  which 
the  style  and  stigma  have  disappeared. 

C,  a  pistil  which  has  grown  into  the 
ripe  bean  pod.   D,  a  ripe  pod  opened 
so  as  to  show  the  arrangement  of  the 
seeds  (beans)  in  the  pod ;  each  seed  (s) 
is  attached  to  a  region  along  the  wall 
of  the  ovary,  known  as  the  placenta 
(pi),  by  means  of  the  base  of  the  old 

ovule.  All  two  thirds  natural  size 


FIG.  16.  Seedling  of  the  peanut 

Below  the  seed  leaves  or  cotyledons  (c)  is 
the  hypocotyl  (K),  from  the  lower  end  of 
which  the  roots  (r)  have  grown ;  from  the 
main  stem  (s)  branches  (br)  and  leaves  (I) 
have  grown ;  at  the  base  of  the  leaves  are 
stipules  (st),  and  at  the  tip  is  the  bud  (6) 


STRUCTURE  AND  WORK  OF  PLANTS  23 

the  ovule.  While  still  within  the  ovule  wall,  the  root,  stem, 
and  leaves  of  the  new  plant  are  formed.  The  ovule  wall  be- 
comes hard,  and,  with  the  new  plant  within  it  and  with  more 
or  less  stored  food,  constitutes  the  seed.  During  the  time  when 
the  seeds  are  developing  the  ovary  also  may  grow  (Fig.  15), 


FIG.  17.  Growth  of  new  plants  from  seeds  of  the  beech  tree 

At  the  left  are  very  young  seedlings,  one  of  which  shows  only  the  seed  leaves 

(cotyledons) ,  the  other  showing  between  the  seed  leaves  a  slender  stalk  which  is 

the  beginning  of  the  stem.   In  the  plants 'at  the  right  the  seed  leaves  still  are 

present,  but  other  leaves  and  the  stems  have  grown  considerably 

23.  Flowers  and  seeds:  the  fruit,  and  seed  germination. 
When  the  seeds  are  ripe  they  may  fall  from  the  ovary,  or 
with  one  or  more  of  the  structures  about  them  they  may  com- 
pose the  so-called  fruit. 

Under  favorable  conditions  the  young  plant  within  the 
seed  bursts  the  seed  coat  and  begins  its  growth.  It  pushes 
out  its  roots,  stem,  and  leaves,  and  soon  assumes  the  ap- 
pearance of  the  kind  of  plant  that  formed  it  (Figs.  16  and  17). 

Details  regarding  the  parts  of  the  plant  and  the  work  they 
do  will  be  treated  in  later  chapters. 


CHAPTER  III 


ROOTS 

24.  Structure  of  roots.  A  very  young  root  is  often  translu- 
cent enough  to  be  examined  directly  with  a  low  power  of  the 
compound  microscope.  It  is  then  seen  to  be  composed  of  an 

exterior  hollow  cortex,  nearly 
cylindrical  in  form,  and  a 
central  cylinder  within  the 
cortex.  The  outermost  por- 
tion of  the  cortex  is  a  layer 
of  somewhat  brick-shaped 
cells  constituting  the  epider- 
mis, and  from  some  of  the 
cells  of  the  epidermis  root 
hairs  often  spring  (Fig.  6). 
The  growing  tip  of  the  root 
is  covered  with  several  layers 
of  cells,  most  of  them  dead 
or  dying,  constituting  the 
root  cap. 

A  moderately  magnified 
cross  section  of  a  very  young 
dicotyledonous  root  shows 

c,  epidermis;  c,  cellular  layer  of  cortex;  the    epidermis    as    a  narrow 

cyl,  central  cylinder ;  w,  woody  strands  of  ring,     Surrounding    a    much 

fibrovascular  bundles  of  central  cylinder.  «          j          •  /•   fi  j 

Alternating  with  these  are  much  smaller  broader  ring   O±    the  Unde 

strands  of  bast  fibers,  not  shown  in  the  dia-  lying  COrtex,  and  within  this 

gram.   Modified  after  Bonnier  and  Sablon  _f  ,       , .     ,  . 

the  central  cylinder,  contain- 
ing a  fixed  number  of  radially  arranged  fibrovascular  bundles. 
The  relative  proportions  of  the  several  regions  can  be  under- 
stood from  Fig.  18. 

24 


. 
:~~  ^ 


FIG.  18.  Diagrammatic  cross  section  of 
a  very  young  dicotyledonous  root 


KOOTS  25 

25.  Uses  of  roots.    It  was  explained  in  Sects.  9  and  10  that 
tvater  is  absorbed  by  roots  and  forced  up  into  the  stem  of  a 
plant  under  considerable  pressure. 

All  plants  must  have  water,  at  any  rate  during  the  part  of 
their  lives  when  they  are  actively  manufacturing  plant  food,  and 
it  is  by  means  of  their  roots  that  most  familiar  plants  absorb 
water  and  the  substances  that  are  dissolved  in  it.  Yet  absorp- 
tion of  water  is  not  the  only  function  of  roots.  They  often  ab- 
sorb oxygen ;  they  commonly  serve  to  anchor  the  plant ;  they 
may  aid  it  to  climb ;  they  frequently  store  food,  water,  or  both ; 
and  in  or  on  them  there  are  sometimes  carried  on  important 
chemical  operations  which  result  in  gaining  material  for  the 
production  of  plant  food  (Sect.  17).  Many  kinds  of  roots  repro- 
duce the  plant ;  that  is,  a  root  or  part  of  one  may  grow  into  a 
new  individual  plant  like  the  one  to  which  the  root  belonged. 

The  great  importance  of  roots  to  life  and  growth  is  well 
shown  by  the  results  which  follow  from  any  severe  injury  to 
the  root  system.  Cut  off  most  of  the  roots  of  a  tree  and  it 
will  die  for  lack  of  water. 

On  the  other  hand,  many  (though  not  all)  kinds  of  trees 
may  be  cut  down  nearly  level  with  the  ground  and  still  sur- 
vive, the  stump  throwing  up  a  vigorous  crop  of  sprouts  which 
grow  into  saplings  that  eventually  replace  the  fallen  trunk. 

The  necessity  of  roots  for  anchorage  is  well  shown  by  Fig.  4. 
In  many  cases  the  power  of  the  roots  to  hold  trees  upright 
is  greatly  increased  by  the  formation  of  buttresses  of  wood, 
which  extend  some  distance  up  the  trunk  from  the  origins  of 
the  larger  roots  (Figs.  259  and  260).  In  some  great  tropical 
trees  these  buttresses  attain  enormous  dimensions. 

26.  Earth  roots.  The  roots  of  most  of  the  higher  plants  with 
which  we  have  practical  dealings,  such  as  forest  trees  and  the 
plants  of  the  orchard,  farm,  and  garden,  are  earth  roots;  that 
is,  they  are  formed,  grow,  and  live  at  a  moderate  distance 
under  ground.    Plants  with  roots  suited  to  life  in  the  earth 
usually  cannot  grow  as  well  in  water  as  in  soil,  and  they  cannot 
grow  at  all  upon  a  bare  rock,  though  sometimes  they  grow 


26  PRACTICAL  BOTANY 

with  their  roots  in  the  crevices  of  rocks.  It  makes  a  great 
difference  to  the  plant  in  what  sort  of  soil  it  grows.  Every 
good  farmer  knows  that  beans  will  thrive  well  in  a  light 
sandy  soil  in  which  corn  or  broom  corn  would  starve.  All 
who  are  familiar  with  the  distribution  of  our  forest  trees 
and  shrubs  have  noticed  that  some  kinds,  such  as  the  spruces, 
most  pines,  the  chestnut,  and  the  jack  oak,  do  well  in  sandy  or 
other  poor  soils.  On  the  other  hand,  the  black  walnut,  the 
tulip  tree,  the  mulberry,  the  Osage  orange,  and  the  papaw 
usually  nourish  only  in  a  deep  rich  soil. 

27.  Direction  and  extent  of  the  root  system.  In  sand  or 
porous  loam  the  root  system  of  the  plant  is  usually  much  more 
extensively  developed  than  in  clay.  If  there  is  a  shallow 
layer  of  loam  overlying  a  shaly  or  clayey  subsoil,  the  roots 
spread  out  horizontally  but  do  not  go  far  down  in  the  earth. 
In  sand,  roots  are  usually  long  and  branch  but  little,  while  in 
rich  soil  they  branch  so  freely  as  to  form  a  close  network.  If 
nutrient  materials  are  irregularly  distributed  in  the  earth  in 
which  a  plant  is  growing,  rootlets  are  so  much  more  exten- 
sively developed  in  the  richer  portions  of  the  soil  that,  as  the 
great  agricultural  chemist  Liebig  forcibly  said,  "  Roots  search 
for  food  as  if  they  had  eyes."  The  various  kinds  of  plants 
differ  .greatly  in  the  general  direction  taken  by  their  roots,  — 
those  of  asparagus,  for  example,  forming  a  sort  of  shallow 
mat,  and  those  of  many  hardwood  trees,  the  radish,  and  the 
sugar  beet  beginning  with  a  single  taproot  which  descends 
for  a  considerable  distance  nearly  or  quite  vertically. 

It  is  impossible  to  get  an  accurate  idea  of  the  root  system 
of  a  very  large  plant,  since  its  length  usually  consists  mainly 
of  slender  fibers  which  are  inextricably  interwoven  with  each 
other  and  penetrate  the  soil  in  every  direction.  The  root  system 
even  of  an  oat  plant,  all  contained  in  a  cubic  yard  or  two  of 
soil,  has  in  one  instance  been  found  to  measure  altogether  over 
450  feet  in  length.  Many  plants  which  ordinarily  have  their 
roots  near  the  surface,  when  grown  in  dry  soils  send  their 
roots  to  great  depths  to  secure  the  needed  water  supply.  In 


ROOTS  27 

some  of  the  drier  parts  of  California  wheat  roots  have  been 
known  to  grow  to  a  depth  of  15  feet  and  the  roots  of  the 
California  poppy  to  a  depth  of  13  feet.  Roots  may  penetrate 
to  much  greater  depths,  those  of  the  mesquite  of  the  South- 
western States  and  Mexico  sometimes  descending  to  reach 
water  as  much  as  60  feet.  It  is  not  difficult  to  get  an  idea  of 
the  extent  of  the  root  system  of  such  a  plant  as  Indian  corn. 
Carefully  dig  away  the  earth  from  one  side  of  the  plant  at  a 
distance  of  about  two  feet,  keeping  a  constant  lookout  for 
smaller  rootlets.  If  none  are  found,  extend  a  trench  com- 
pletely about  the  plant  at  the  distance  already  used  as  a 
radius.  Make  the  trench  about  two  feet  deep  and  stand  a 
piece  of  poultry  netting  in  it,  so  as  to  make  a  circular  fence 
about  the  roots  of  the  plant.  Run  some  wire  stakes  crosswise 
through  the  mass  of  roots,  so  as  to  reach  across  its  entire 
diameter.  With  a  stream  of  water  from  a  garden  hose  or  with 
numerous  pails  of  water  wash  away  the  earth  as  completely 
as  possible  from  the  mass  of  roots  and  remove  the  root  system 
entire.  It  may  then  be  used  for  illustration  in  the  schoolroom. 
28.  Pull  exerted  by  roots.  After  root  fibers  or  the  taproots 
of  herbaceous  plants  have  attained  their  full  length,  in  many 
kinds  of  plants  a  decided  shortening  of  the  root  takes  place. 
This  shortening  originates  in  the  cellular  portion  of  the  cor- 
tex, between  its  outer  layers  and  the  central  cylinder  of  the 
root,  and  it  may  amount  to  from  10  to  25  per  cent  of  the 
length  of  the  root  before  contraction.  Because  the  epidermis 
does  not  contract,  its  outer  surface  often  becomes  much  wrin- 
kled, especially  in  the  roots  of  bulbous  plants.  The  shorten- 
ing of  the  fibrous  roots  which  spring  from  a  taproot  holds  it 
firmly  in  place,  as  a  derrick  is  held  upright  by  guy  ropes. 
Sometimes,  as  in  the  dandelion,  the  taproot  shortens  about 
as  fast  as  the  short  stems  which  crown  the  root  grow  upward. 
In  this  way  the  rosette  of  leaves  is  kept  firmly  pressed  against 
the  ground,  or  it  may  even  be  drawn  slightly  into  the  e.arth. 
Grass  jolants  on  a  lawn  are  injured  or  destroyed  by  being  de- 
prived of  light  by  the  rosette  of  dandelion  or  fall  dandelion. 


28  PEACTICAL  BOTANY 

29.  Effects  of  roots  on  the  soil.  If  we  dig  up  a  spadeful  of 
earth  from  a  well-grassed  meadow,  or  from  a  little  inside  the 
circumference  of  the  circle  formed  by  the  roots  of  a  tree,  we 
shall  find  the  soil  bound  together  by  the  living  roots  or  full  of 
little,  crooked,  tubular  channels  left  by  the  decay  of  dead  ones. 
Thus  the  soil  is  in  the  one  case,  held  together  so  as  to  pre- 
vent its  becoming  gullied  and  washed  away  by  rains,  and  in 
the  other  case  made  more  porous  and  easily  penetrated  by  air 
and  water.  The  latter  effect  is  a  very  important  one  in  the 
case  of  stiff  clay  soils,  which  when  closely  packed  are  almost 
waterproof. 

The  extensive  washing  away  of  soils  when  unprotected  by 
a  covering  of  plants,  such  as  grass,  shrubs,  or  forest  growth,  is 
one  of  the  most  serious  calamities  that  can  befall  a  country. 
It  is  especially  formidable  in  hilly  regions,  which  may  become 
wholly  uninhabitable  if  the  forests  are  cut  off  and  the  turf  on 
the  hillsides  is  destroyed  by  too  constant  grazing  and  tram- 
pling of  sheep  or  goats.  Immense  areas  of  land  once  valuable 
for  timber  and  for  grazing  have  thus  been  ruined  throughout 
southern  Europe,  and  the  same  process  is  under  way  in  our 
own  country  all  the  way  from  New  England  to  the  Pacific 
coast  region.  One  of  the  clearest  ways  in  which  the  loss  by 
washing  away  of  the  soil  can  be  presented  is  by  considering 
how  the  land  is  carried  into  the  sea  by  great  rivers.  The  delta 
of  the  Mississippi  covers  an  area  of  more  than  12,000  square 
miles.  It  consists  of  material  brought  down  by  the  river  in 
the  form  of  mud,  now  forming  a  deposit  of  unknown  thick- 
ness, probably  averaging  more  than  500  feet.  It  is  calculated 
that  the  river  every  vear  carries  enough  solid  matter  to  form 
a  layer  one  foot  thick  over  an  area  of  about  268  square  miles. 
Remembering  that  this  mud  consists  mainly  of  the  choicest 
part  of  the  rich  soil  of  the  Mississippi  basin,  it  is  easy  to  see 
that  the  land  is  robbed  every  year  of  the  material  to  support 
enormous  harvests  x  (see  Chapter  XXIV). 

1  See  "Forest  Influences,"  Bulletin  7,  Division  of  Forestry,  U.  S.  Dept 
Agr.,  1893. 


BOOTS 


29 


30.  Relation  of  earth  roots  to  air  and  water.  The  soil  at 
moderate  depths  contains  much  air  in  its  pores,  the  amount 
being  largest  in  light  loams  and  sand,  and  least  in  stiff  clays. 
This  air  is  essential  to  the  health  and  growth  of  ordinary 
roots.  Many  kinds  of  plants  growing  in  earth  are  quickly 
killed  when  transferred  to  a  glass  battery  jar  with  a  lead  cover 
sealed  on,  if  water  enough  is  poured  in  through  a  thistle  tube 


FIG.  19.  Cypress  trees  (Taxodium)  growing  in  a  swamp 

The  conical  "  knees  "  growing  from  the  roots  and  nearly  always  above  water  are 
thought  to  serve  as  channels  to  supply  air  to  the  roots 

to  fill  the  jar  almost  to  the  exclusion  of  air.  In  the  same  way, 
if  water  is  backed  up  a  stream  when  a  dam  is  built  across  it, 
most  of  the  trees  that  are  surrounded  by  the  pond  formed  by 
the  retained  water  are  killed.  They  have  been  drowned,  and 
die  for  lack  of  air.  Even  the  lower  forms  of  green  plants 
(Figs.  156-168)  will  soon  die  for  lack  of  it,  if  kept  in  a 
tightly  stoppered  jar  or  bottle  full  of  water.  Most  aquatic 
plants  which  have  leaves  or  green  stems  exposed  to  the  air  — 
like  pond  lilies,  some  rushes,  cat-tails,  and  so  on  —  convey  air 
down  into  the  submerged  parts  by  means  of  numerous 


30  PRACTICAL  BOTANY 

air  passages,  which  lead  from  the  leaf,  through  the  stem, 
down  into  the  roots  (Fig.  360).  It  is  supposed  that  "  cypress 
knees,"  curious  outgrowths  from  the  roots  of  the  American 
cypress  (Fig.  19),  absorb  air,  which  passes  down  into  the  roots. 
A  supply  of  water  is,  as  already  suggested,  even  more 
evidently  necessary  for  earth  roots  than  is  a  supply  of  air. 
The  appearance  during  a  drought  of  fields  planted  with  ordi- 
nary crops  is  familiar  to  most  people.  The  dwarfed  condi- 
tion to  which  plants  can  be  brought  by  a  scanty  supply  of 
water  is  less  well  known.  Many  annuals;  if  given  barely 
enough  water  to  keep  them  alive,  will  flower  and  bear  seed 
after  reaching  a  height  of  hardly  a  greater  number  of  inches 
than  they  would  measure  in  feet  under  favorable  conditions. 
When  the  water  supply  is  wholly  withheld  from  ordinary 
potted  plants  they  soon  wilt  and  die,  as  every  one  knows. 

31.  Water  roots.   Most  aquatic  perennials,  like  the  cat-tails, 
arrowheads,  pickerel  weeds,  pond  lilies,   and  many  grasses 
and  sedges,  form  mainly  earth  roots.    On  the  other  hand,  some 
plants  not  aquatics,  as  many  willows,  can  develop  roots  indif- 
ferently either  in  earth  or  in  water.  A  row  of  willows  along  a 
brook  usually  sends  great  numbers  of  roots  into  the  earth,  and 
also  produces  a  multitude  of  fibrous  roots  which  dangle  in  the 
water  of  the  brook.    Cuttings  of  Wandering  Jew  {Zebrinci), 
geranium  (Pelargonium),  and  many  other  common  plants,  root 
readily  in  water,  and  grow  for  a  long  time  if  supplied  only  with 
ordinary  river  or  well  water.  The  number  of  kinds  of  seed  plants 
which  float,  and  therefore  produce  only  water  roots  (if  they  have 
roots  at  all),  is  rather  small.    Some  of  the  commonest  are  the 
so-called  "water  hyacinth"  and  the  little  duckweeds  (Fig.  357) 
so  often  seen  on  the  surface  of  stagnant  pools  and  streams. 

32.  Air  roots.  Roots  may  be  produced  by  portions  of  the 
stem  above  ground,  in  the  case  of  plants  which  root  in  the 
earth.    Well-known  examples  of  these   are  the  brace  roots 
of  corn,  often  originating  a  foot  or  more  above  the  earth  and 
usually  at  length  extending  into  the  soil,  and  the  tough, 
fibrous  roots  by  means  of  which  English  ivy  and  poison  ivy 


KOOTS 


31 


FIG.  20.  Aerial  roots  of  an  orchid  (Cattleya) 

(Fig.  46)  climb.  Air  roots  are  also  borne  by  many  kinds  of  air 
plants  which  do  not  root  in  the  earth  at  all.  Such  plants  are 
usually  natives  of  moist,  warm  climates.  Good  examples  of 
air  plants  are  many  orchids  (Fig.  20),  and  some  plants  of  the 


FIG.  21    Aerial  roots  of  a  wild  tig  tree  and  lianas  in  a  tropical  forest 


BOOTS 


33 


Pineapple  family.  Aerial  orchids  frequently  possess  roots  of 
peculiar  structure,  covered  with  a  papery,  absorbent  layer 
which  takes  up  water  freely  when  exposed  to  rain  or  dew. 
One  air  plant,  the  Spanish  moss  (Tillandsia)  (Figs.  367,  368), 
common  in  the  Gulf  States,  has  no  roots, 
but  it  imbibes  water  freely  by  means  of 
special  absorbing  hairs  scattered  over  the 
surface  of  the  plant.  The  Tillandsia  is  a 
characteristic  feature  of  many  Southern 
regions,  often  appearing  as  tangled,  rope- 
like  masses  hanging  from  the  trees. 

33.  Reproduction   by   means   of   roots. 
Roots  are  often  capable  of  producing  buds 
which  may  develop  into  new  individuals 
and  thus  serve  to  propagate  the  plant. 
The  sweet  potato  is  a  good  instance  of 
this,  each  root  if  buried  in  moist  sand 
being  capable   of  giving  rise  to   several 
new  plants  (Fig.  22).    Roses  are  propa- 
gated by  root  cuttings,  and  some  trees, 
such  as  the  silver-leaved  poplar  (Populus) 
and  the  black  locust  {Robinia),  are  very 
troublesome  because  of  the  readiness  with 
which  young  sprouts  (sometimes  called 
suckers)  spring  up  from  the  roots.    Many 
bad  weeds,  such  as  the  field  sorrel  (Rumex) 
and   the  Canada   thistle   (Cirsium),    are 
reproduced  by  roots.    In  case  of  desirable 
plants  that  can  be  propagated  either  by 

pieces  of  root  or  by  seeds,  it  is  generally  better  to  use  root 
cuttings,  as  they  will  grow  much  faster. 

34.  Duration  of  life  and  storage  of  food  and  water  in  roots. 
It  is  usual  to  divide  plants  according  to  their  duration  of  life 
into  three  classes :  annuals,  living  one  year  or  less ;  biennials, 
living  two   years;  perennials,  living  more  than  two  years. 
The  boundaries  between  these  classes  are  not  always  definite ; 


FIG.  22.  Vegetative 

reproduction  of  the 

sweet  potato 

The  potato  was  buried  in 
moist  sand  and  began  to 
sprout,  that  is,  to  send 
out  shoots  from  adven- 
titious buds  at  various 
points.  Each  shoot  may 
grow  into  a  new  plant. 
About  half  natural  size 


34 


PRACTICAL  BOTANY 


for  example,  winter  wheat  is  an  annual,  though  it  does  not 
seed  until  the  next  summer  after  it  is  planted.  And  the  cot- 
ton plant,  the  lima  bean,  the  tomato,  and  the  castor  bean  are 
instances  of  plants  which  with  us  are  cultivated  as  annuals, 
but  in  warm  climates  live  several  years ;  the  castor  bean,  in- 
deed, grows  there  into  a  large,  almost  tree-like  shrub.  Very 
commonly  plants  which  live  for  more  than  one  year  have  food 
stored  in  their  roots.  j 


FIG.  23.  Clustered,  fleshy  roots  of  the  dahlia,  with  much  stored  plant 
food,  in  early  spring 

st,  remains  of  last  year's  stem ;  sh,  young  shoots  beginning  to  sprout  from 
the  upper  ends  of  the  roots.   One  fourth  natural  size 

Such  biennials  as  beets,  carrots,  and  parsnips  store  up  much 
food  in  the  root1  during  the  first  summer's  growth,  and  form 
a  large  tuft  or  rosette  of  leaves,  but  do  not  develop  much  stem 
above  ground.  During  the  second  summer  the  stored  food  is 
consumed  in  the  production  of  leafy  stems,  bearing  flowers 
and  fruit,  and  in  the  autumn  the  root  appears  quite  withered 
and  nearly  dry. 

1  The  underground  part  of  the  carrot  and  the  parsnip  is  part  stem  and 
part  root. 


ROOTS  35 

Herbaceous  perennials,  like  the  dahlia  (Fig.  23)  and  the 
common  rhubarb,  store  food  in  the  root  during  the  summer, 
and  consume  part  or  all  of  it  in  the  growth  of  the  following 
spring.  Trees  and  shrubs  in  temperate  or  cold  climates  store 
starch  and  other  foods  in  the  roots,  as  well  as  the  stem,  dur- 
ing the  winter.  It  is  the  stored  food  in  the  root  that  enables 
such  plants  as  rhubarb,  the  peony,  some  buttercups,  sweet 
cicely,  the  dandelion,  and  many  others  to  make  a  quick  growth 
in  the  spring  before  the  weather  is  warm  enough  for  the  man- 
ufacture of  much  plant  food.  The  starch,  sugar,  and  proteins 
which  abound  in  many  roots  or  root-like  portions  of  plants 
make  them  valuable  for  food,  as  in  the  case  of  beets,  turnips, 
carrots,  parsnips,  sweet  potatoes,  salsify,  and  in  the  cassava 
plant,  from  which  tapioca  is  made. 

It  is  frequently  the  case  that  desert  plants  store  large 
quantities  of  water  in  their  roots  or  in  combinations  of  roots 
and  underground  stems,  and  are  thus  able  to  survive  long 
periods  without  rain. 

35.  Roots  in  relation  to  other  organisms.  The  roots  of  the 
higher  plants  often  enter  into  complicated  relations  with  plants 
of  other  species  or  with  animals.    Before  discussing  these  re- 
lations it  is  necessary  to  state  briefly  what  some  of  them  are. 
A  plant  or  animal  which  feeds  in  whole  or  in  part  on  the  sub- 
stance of  another  living  organism  is  called  a  parasite.  Familiar 
examples  of  animals  parasitic  on  other  animals  are  fleas  and 
ticks.    The  organism  which  supports  a  parasite  is  called  the 
host.    Organisms  which  live  together  in  a  mutually  helpful 
way  are  said  to  be  mutualists  or  sometimes  are  called  mess- 
mates.   Roots  may  be : 

(1)  Parasitic  on  other  roots  or  stems. 

(2)  Hosts  for  parasitic  roots. 

(3)  Hosts  for  parasitic  animals. 

(4)  Messmates  or  mutualists  with  other  organisms. 

36.  Parasitic  roots.  A  good  many  of  the  higher  plants  feed 
altogether  or  partially  on  the  sap  which  they  draw  from  other 
living  plants.    Those  which  live  entirely  at  the  expense  of  the 


36  PRACTICAL  BOTANY 

host  are  total  parasites,  while  the  others  are  partial  parasites. 
The  dodders  (Fig.  351)  are  practically  leafless,  of  a  yellow- 
greenish  or  whitish  color,  and  incapable  of  photosynthesis. 
The  mistletoes  and  many  other  half  parasites  have  green 
leaves  and  can  do  photosynthetic  work,  so  that  they  may 
depend  on  the  host  only  for  water  and  mineral  subtances,  but 
make  for  themselves  starch  or  other  carbohydrates  from  the 
raw  materials.  Root  parasites  (Fig.  309)  are  often  attached 
to  the  roots  of  the  host  at  some  distance  from  the  stem  of 
the  latter,  so  that  few  but  botanists  recognize  the  real  state 
of  the  relations  between  the  two  plants.  The  sucking  roots 
of  parasites,  known  as  haustoria,  are  of  peculiar  structure  and 
have  the  power  of  penetrating  rapidly  into  the  substance  of 
the  host.  In  the  dodder,  at  any  rate,  this  power  is  partly  due 
to  the  presence  of  ferments,  liquid  or  semi-liquid  substances 
manufactured  by  the  haustorium  and  capable  of  dissolving 
cellulose. 

37.  Partnership  of  roots  and  bacteria.  Bacteria  are  exceed- 
ingly minute  plants  of  very  low  organization  (Fig.  150). 
Their  forms  and  structure  are  shown  in  a  general  way  by  the 
figure.  They  differ  greatly  in  their  habits  of  life,  as  is  shown 
in  Chapter  XL  Those  which  inhabit  little  tubercles  on  the 
roots  of  most  leguminous  plants  (as  those  of  the  Pea  family 
are  called)  are  of  the  highest  value  to  the  farmer.  The  tu- 
bercles occur  in  the  greatest  abundance,  4572  having  been 
counted  on  the  roots  of  a  single  pea  plant.  Fig.  305  shows 
their  mode  of  occurrence  on  the  roots  of  red  clover.  Each 
tubercle  contains  multitudes  of  root  tubercle  bacteria,  which 
are  able  to  change  the  free  nitrogen  of  the  air,  contained 
in  the  pores  of  the  soil,  into  a  combined  form  in  which  it  can 
be  absorbed  by  the  plant.  Without  the  action  of  these  or 
other  bacteria  or  other  agents  to  transform  atmospheric  nitro- 
gen into  a  soluble  form  it  is  perfectly  useless  to  the  higher 
plants.1 

1  It  is  certain  that  other  bacteria  besides  those  of  root  tubercles  render 
nitrogen  available,  but  the  extent  of  their  action  is  not  fully  known. 


BOOTS  37 

In  order  to  ascertain  how  much  nitrogen  is  produced  by  any 
given  crop  it  is  necessary  to  make  chemical  analyses  of  care- 
fully selected  and  weighed  samples  of  the  clover,  alfalfa,  or 
other  crop  studied.  In  this  way  it  was  found  in  one  series  of 
experiments  that  a  single  crop  of  alfalfa  yielded  95  pounds, 
red  clover  102  pounds,  and  crimson  clover  134  pounds  to  the 
acre.  As  about  two  thirds  of  this  nitrogen  is  taken  from  the 
air  by  the  plant,  turning  under  by  plowing  any  of  these  legu- 
minous crops  adds  greatly  to  the  available  nitrogen  of  the  soil. 
A  ton  of  barnyard  manure  contains  only  about  10  pounds  of 
nitrogen.  Therefore  an  acre  of  alfalfa  plowed  under  might 
add  to  the  soil  as  much  nitrogen  as  could  be  gained  from  16 
tons  of  manure,  though  the  manure  would  add  other  desired 
substances  to  the  soil.  A  crop  of  corn  of  50  bushels  per  acre 
would  remove  from  the  soil  (in  both  grain  and  fodder)  about 
74  pounds  of  nitrogen  per  acre.  A  wheat  crop  of  25  bushels 
per  acre  would  remove  from  the  soil  about  48  pounds  of 
nitrogen  per  acre.  Experiments  continued  for  a  series  of  years 
upon  worn-out  land,  treated  year  after  year  with  lime  and 
leguminous  crops  plowed  under,  show  great  gains  in  fertility. 
In  one  set  of  experiments  lasting  from  1902  to  1907  the  soil 
which  had  been  thus  treated  produced  a  little  more  than  six 
times  as  large  a  crop  of  oats  as  a  similar  untreated  area.  On 
common  prairie  land  in  Illinois  the  value  of  the  nitrogen 
gained  by  the  root  tubercles  of  a  single  crop  of  alfalfa  was 
found  to  amount  to  $25.80  per  acre,  reckoning  the  nitrogen 
as  worth  the  usual  fertilizer  price  for  it,  15  cents  per  pound. 
What  part  of  this  improvement  is  due  to  better  cultivation  is 
a  matter  still  under  discussion.  The  poorer  the  land  is  in 
nitrogen  the  more  effective  is  this  process  of  "green  manur- 
ing "  with  leguminous  crops.  Provided  the  tubercle  bacteria 
are  present,  clover  can  make  a  vigorous  growth  without  any 
soluble  nitrogen  in  the  soil  at  the  beginning.1 

1  On  the  general  subject  of  maintenance  of  fertility  by  plowing  under 
leguminous  crops,  see  Hopkins,  Soil  Fertility  and  Permanent  Agriculture, 
chap,  xvi,  and  Part  III.  Ginn  and  Company,  Boston. 


38 


PRACTICAL  BOTANY 


38.  Partnership  of  roots  and  filaments  of  fungi.  Many  of  the 
flowerless  plants  known  by  the  general  name  of  fungi  form 
a  dense  network  of  very  minute  threads.  Such  a  network  is 
found  in  intimate  association  with  the  roots  of  many  kinds  of 
flowering  plants.  It  is  especially  com- 
mon on  the  roots  of  those  which  cannot 
manufacture  plant  food  by  photosyn- 
thesis, but  it  also  occurs  on  other  plants 
with  green  leaves,  such  as  pines  and 
beeches.  On  the  roots  of  the  beech 
the  fungus  filaments  are  found  united 
into  a  sort  of  membrane,  covering  the 
tips  of  the  young  roots  and  extend- 
ing back  for  a  considerable  distance 
(Fig.  24).  In  such  plants  as  the  heaths, 
blueberries,  and  their  relatives,  the 
fungus  threads  form  little  tangled 
masses  inside  the  cells  near  the  sur- 
face of  the  root  and  send  out  free  ends 
into  the  surrounding  soil.  In  any  case 
the  whole  filamentous  mass  living  in 
connection  with  the  root  is  called  a 
mycorrhiza.  Roots  provided  with  my- 
corrhiza usually  form  few  or  no  root  hairs,  and  it  is  supposed 
that  the  fungus  threads  to  some  extent  perform  the  work  of 
root  hairs  in  absorbing  soil  water.  The  subject  is  not  yet 
well  understood,  but  it  would  seem  that  certain  trees,  such  as 
pines  and  oaks,  do  not  flourish  as  well  when  grown  in  a  soil 
which  does  not  develop  a  mycorrhiza  upon  their  roots.1 

i  See  "Experiments  in  Blueberry  Culture,"  Bulletin  193,  Bureau  of  Plant 
Industry,  U.S.  Dept.  Agr. 


FIG.  24.   Tip  of  a  root  of 

European  beech,  covered 

with  mycorrhiza 

The  coating  has  been  stripped 
off  for  a  little  way  at  the 
top  to  show  the  thickness  of 
the  mycorrhiza.  Magnified 
30  diameters.  After  Pfeffer 


CHAPTER  IV 
THE  STEM  AND  THE  LEAF 

39.  Stem  and  leaf  as  coworkers.  In  a  general  way  it  may 
be  said  that  the  stem  and  the  leaf  together  do  the  work  of 
making  plant  food  from  the  raw  materials  (Sect.  17).    In 
most  of  our  commonest  seed  plants  the  stem  is  mainly  impor- 
tant as  the  part  of  the  plant  body  which  bears  leaves,  maintains 
them  in  the-  most  advantageous  position  to  receive  sunlight, 
carries  to  them  water  and  dissolved  salts  from  the  earth,  and 
carries  away  from  the  leaves  the  newly  made  plant  food  which 
is  to  serve  for  the  immediate  needs  of  the  plant  body  or  to  be 
stored  for  use  later  on.   The  stem  and  the  leaf  are  so  intimately 
associated  that  it  is  often  convenient  to  have  a  single  name 
for  the  two  together.    The  stem  and  its  leaves  collectively 
are  known  as  the  shoot. 

40.  Photosynthesis  done  by  stems.  In  some  practically  leaf- 
less plants,  such  as  the  cacti,  the  photosynthetic  work  of  the 
plant  is  all  done  by  the  stem,  which  is  covered  with  layers  of 
chlorophyll-containing  cells.    Stems  flattened  so  as  to  expose 
a  good  deal  of  surface  for  photosynthesis  are  shown  in  Fig.  25 
and  still  more  expanded  ones  in  Fig.  26.   In  the  shrubs  known 
as  switch  plants  (Fig.  365),  common  in  some  regions  where 
the  summers  are  hot  and  almost  rainless,  the  leaves  (if  there 
are  any)  are  borne  for  only  a  few  months  of  the  year,  usually 
in  the  spring.    During  the  rest  of  the  year  photosynthesis  is 
slowly  carried  on  by  the  green  layer  of  the  bark,  which  is 
abundantly  supplied  with  chlorophyll.    Even  among  the  trees 
and   shrubs   of   temperate   North  America   there  are  many 
species,  such  as  the  wahoo,  box  elder,  sassafras,  and  some 
roses,  which  have  much  green  bark  on  the  younger  twigs  and 
probably  accomplish  a  good  deal  of  photosynthesis  through 

39 


40 


PRACTICAL  BOTANY 


these.  As  the  twigs  grow  older  the  green  layer  is  shut  away 
from  the  light  by  the  corky  layer  outside  of  it  and  soon  dies. 
Most  of  our  useful  annuals  of  the  farm  and  garden, 
such  as  corn,  potatoes,  tomatoes,  squashes,  and  so  on, 
have  green  stems  which  do  photosynthetic  work. 

41.  The  stem  raises  leaves  into  the  light.     Many 
plants  which  cover  the  ground  rather  closely  do  not 

need  to  raise  them- 
selves much  from 
the  earth  in  secur- 
ing their  share  of 
the  light.  Good 
examples  of  these 
are  such  familiar 
creeping  plants  as 
white  clover,  black 
medic  (Medicago), 
moneywort  (Lysi- 
macliia),  and  some 
species  of  wild  ev- 
erlasting (Anten- 
naria).  But  very 
commonly  plants 
compete  for  light 
against  each  other, 
as  may  readily  be 
seen  in  almost  any 
cornfield.  When 
the  corn  is  only  a 
little  way  above 
ground  it  is  neces- 
sary to  keep  it  free 
from  rank,  quickly 
FIG.  25.  Branches  of  Muehlenbeckia,  a  plant  with  ffrowmp-  weeds  by 
flattened  stems  which  do  most  of  the  photosynthetic  °  °  J 

work  of  the  plant  frequent  cultiva- 

/,  flowers;  I,  leaves;  s,  stems.   One  half  natural  size         tion.   If  this  Work 


THE  STEM  AND  THE  LEAF 


41 


is  neglected,  the  young  corn  plants  will  be  overshadowed  and 
dwarfed  and  the  crop  greatly  injured.  But  as  soon  as  the 
cornstalks  have  lengthened  enough  to  carry  the  spreading 
leaves  above  the  tops  of  ordinary  weeds  and  leave  them  in 
the  shade,  the  corn  plants  are  safe  from  further  competition 
with  these  plants,  though  other  species  that  can  thrive  in  weak 
light  may  develop  later.  In  the  same  way  wild  plants  kill  off 
other  species  by  overshadowing  them.  Under 
a  close  thicket  of  dogwoods  (  Cornus),  hazels, 


FIG.  26.  Stem  of  "smilax"  (Myrsiphyllum) 

I,  scale-like  leaves;  cl,  cladophyll,  or  leaf-like  branch,  growing  in  the  axil  of  a 
leaf;  ped,  flower  stalk,  growing  in  the  axil  of  a  leaf 

or  buttonbush,  hardly  any  smaller  plants  can  grow,  and  the 
most  successful  competitors  with  the  bushes  are  such  climbers 
as  the  cat  brier  {Smilax,  Fig.  49),1  climbing  false  buckwheat 
(Polygonum),  wild  morning-glory,  and  climbing  hemp  weed 
(Mikania).  These  support  themselves  on  the  bushes  or  other 
plants,  and  secure  all  the  light  they  need  by  running  along 
the  tops  of  the  supporting  plants. 

1  This  is  not  the  familiar  greenhouse  plant  shown  in  Fig.  26,  which  is 
usually  called  smilax  by  florists. 


42 


PEACTICAL  BOTANY 


As  a  result  of  competition  with  each  other  to  secure  light, 
plant  stems  often  become  greatly  lengthened.  Any  one  who 
is  observant  and  familiar  with  things  out  of  doors  must  have 
noticed  the  different  form  (habit  it  is  called  by  botanists)  of 

such  plants  as  giant  ragweed 
(^Ambrosia)  or  hemp  as  they 
grow  tall  and  little-branched 
when  in  dense  clumps,  or  low 
and  spreading  when  they  stand 
singly.  And  full-grown  trees 
such  as  pines  are  nearly  branch- 
less for  most  of  their  height, 
when  growing  in  dense  forests, 
but  low  and  broad-topped  with 
many  lateral  branches  when 
growing  alone  in  a  pasture 
(Fig.  246).  A  tree  growing  on 
the  edge  of  a  patch  of  dense 
woods  may  develop  the  pasture 
habit  on  its  exposed  side  and 
the  forest  habit  on  the  side 
toward  the  woods,  like  the  tree 
in  Fig.  27. 

42.  Danger  from  excessive 
height  of  stems.  Wheat,  oats, 
or  corn  plants  are  sometimes 
blown  down  by  severe  winds, 
and  a  field  of  grain  in  this  con- 
dition is  said  to  be  "  lodged." 
Large  tracts  of  forest  may  also 
be  greatly  damaged  by  severe 
storms,  particularly  when  the 
trees  are  loaded  with  sleet  (Fig.  28),  and  the  area  covered  with 
broken-down  tree  trunks  is  known  as  a  "  windfall."  But  neither 
tall  grain  nor  forest  trees  can  be  blown  down  as  easily  when 
growing  massed  together  as  when  standing  singly,  since  every 


FIG.  27.  Pruning  as  an  effect  of 
shade 

The  large  American  beech  in  the  fore- 
ground has  developed  no  considerable 
limbs  on  the  right,  because,  until  it 
was  well  grown,  another  beech  stood 
within  fourteen  feet  of  it,  on  that  side 


THE  STEM  AND  THE  LEAF 


43 


FIG.  28.  Cottonwood  trees  on  the  day  after  a  sleet  storm 
Many  branches  have  been  broken  off  by  the  weight  of  the  sleet 

individual  in  the  interior  of  the  field  or  forest  is  much  sheltered 
from  the  wind  by  its  neighbors,  and  all  together  present  enough 
resistance  partially  to  impede  the  wind.  Scientific  foresters  in 
clearing  the  trees  off  a  large  tract  begin  on  the  sheltered  side  and 
cut  toward  the  quarter  from  which  severe  storms  usually  come. 


44  PRACTICAL  BOTANY 

43.  Growth    in    length.    Under   favorable    conditions    the 
younger  portions  of  the  stem  for  a  good  while  increase  con- 
tinually in  length.    The  rate  of  growth  varies  greatly  in  dif- 
ferent plants :  sunflowers  and  giant  ragweed  (Artemisia)  may 
grow  to  a  height  of  10  or  12  feet,  and  climbers  like  gourds 
and  hops  to  a  length  of  perhaps  40  feet,  in  a  single  summer. 
On  the  other  hand,  pine  seedlings  during  their  first  summer 
only  grow  to  be  from  1  to   3   inches  high,  and  oak  seed- 
lings less  than  5  inches.     The  growth  per  year  for  a  time 
continues  to  increase  and  then  diminishes.    For  example,  the 
long-leaf  pine  (Fig.  261)  grows  only  about  three  quarters 
of  an  inch  the  first  year.    For  the  first  fifty  years  it  makes 
an  average  annual  growth  of  14  or  15  inches;  for  the  next 
fifty,  4  or  5  inches ;  and  from  one  hundred  years  to  extreme 
old  age,  about  one  and  one-half  inches.  It  usually  lives  about 
two  hundred  years. 

The  growth  of  the  younger  nodes  of  most  plants  is  quite  un- 
equal, as  may  be  learned  from  the  study  of  a  rapidly  growing 
stem,  such  as  the  morning-glory.1  It  will  also  prove  interest- 
ing to  measure  such  plants  as  corn,  broom  corn,  hemp,  and 
pole  beans,  to  determine  whether  they  elongate  more  during 
the  day  or  the  night,  and  during  warm  or  cool  weather. 

44.  Internal  structure  of  the  young  dicotyledonous  stem.2 
The  structure  of  the  fully  developed  stem  can  best  be  under- 
stood by  tracing  its  development  from  the  time  when  the  em- 
bryo begins  to  grow  in  the  sprouting  seed.    That,  however,  is 
a  rather  difficult  process  to  follow,  so  this  brief  account  will 
begin  with  the  stem  already  considerably  developed. 

In  common  language  the  dicotyledonous  stem  is  said  to  con- 
sist of  bark,  wood,  and  pith.  These  regions  are  very  distinctly 


1  See  Bergen  and  Davis1  s  Principles  of  Botany,  p.  17. 

2  See  also  Sects.  45-48.   The  stem  of  many  gymnosperms  (e.g.  trees  of 
the  Pine  family)  in  its  general  structure  much  resembles  the  dicotyledon- 
ous stem.   For  a  general  account  of  the  stem  structure  of  dicotyledons  and 
monocotyledons  see  Coulter,  Barnes,  and  Cowles's  Textbook  of  Botany, 
chap,  iv,  A.  ANGIOSPERMS. 


THE  STEM  AND  THE  LEAF 


45 


seen  in  the  youngest  twigs  of  most  of  our  dicotyledonous 
trees  and  shrubs,  such  as  willow,  poplar,  sassafras,  and  elder. 
The  early  structure  of  dicotyledonous  stems  is  in  some  ways 
best  shown  in  the  stems  of  woody  climbers.  Fig.  29  shows 


e    b    c  p 

EIG.  29.  Diagrammatic  cross  section  of  one-year-old  Aristolochia  stem 

e,  region  of  epidermis ;  6,  hard  bast ;  o,  outer  or  bark  part  of  a  bundle  (the  cellular 
portion  under  the  letter) ;  w,  inner  or  woody  part  of  bundle ;  c,  cambium  layer ; 
p,  region  of  pith ;  m,  a  medullary  ray.  The  space  between  the  hard  bast  and  the 
bundles  is  occupied  by  thin-walled,  somewhat  cubical  cells  of  the  bark.  Consid- 
erably magnified 


FIG.  30.  Diagrammatic  cross  section  of  sunflower  stem 

p,  pith ;  fv,  woody  or  fibrovascular  bundles ;  e,  epidermis ;  b,  bundles  of  hard  bast 
fibers  of  the  bark.   Somewhat  magnified.  After  Frank 

the  relative  position  of  the  structural  components  of  the  one- 
year-old  stem  of  Dutchman's-pipe,  as  seen  in  a  cross  section. 
The  outer  cylinder  (e-c)  is  bark ;  the  central  portion  (^?)  is 
pith.  Between  bark  and  pith,  extending  both  inward  and  out- 
ward from  the  cambium  layer  (<?),  are  fibrovascular  bundles 
(0-w),  seven  of  which  are  shown  in  the  figure.  Each  bundle 


46 


PRACTICAL  BOTANY 


consists  of  a  cellular  portion  (0)  which  belongs  to  the  bark 
system,  and  a  fibrous  and  tubular  portion  (w)  which  belongs 
to  the  wood  system.  Briefly  stated,  the  uses  of  some  of 
the  several  parts  are  as  follows :  (1)  The  epidermis  serves  as 

a  protective  covering  for  the 
young  stem,  and  to  a  consider- 
able extent  prevents  it  from 
becoming  dried  up. 

(2)  The  layers  of  cork  cells 
soon  formed  close  beneath  the 
epidermis  (not  separately  shown 
in  the  diagram)  prevent  loss  of 
water  and  consequent  drying  up. 

(3)  The  layers  of  green  cells 
which  at  first  directly  underlie 
the  epidermis   (not  shown  in 
the  diagram)  are  useful  in  the 
manufacture  of  plant  food.1 

(4)  The  fibrous  cells  of  the 
hard  bast  (6)  give  toughness  to 
the  stem. 

(5)  The   thin-walled    tubes 
of  the  outer  portions  (0)  of  the 
bundles     carry    manufactured 


The  tubes  with  spiral  markings  (spiral 
vessels)  are  the  principal  channels  for 
the  conduction  of  water.  Between  and 
around  them  are  thin-walled  nucle- 
ated cells,  containing  much  cell  sap. 
Much  magnified.  After  Frank 


FIG.  31.  Lengthwise  section  through 

the  vascular  part  of  a  fibrovascular 

bundle  of  sunflower  stem 

plant  food  in  liquid  form  down- 
ward or  toward  the  roots. 

(6)  The  cambium  layer  (<?) 
(shown  proportionally  thicker 
in  the  diagram  than  it  really  is) 
grows,  and  on  its  outer  side  it  forms  new  bark,  while  on  its 
inner  side  it  forms  new  wood  (see  Sect.  47). 

(7)  The  woody  portions  (w)  of  the  bundles  carry  water 
upward  or  toward  the  leaves.  The  fibers  which  constitute  a 
considerable  portion  of  the  wood  part  of  the  bundles  both 
stiffen  the  stem  and  make  it  tougher. 

1  See  Sect.  40. 


THE  STEM  AND  THE  LEAF 


47 


One-year-old  stems  of  dicotyledonous  plants  which  are  not 
climbers  usually  differ  in  structure  from  the  type  shown  in 
Fig.  29  mainly  in  having  the  bundles  more  or  less  completely 
joined  into  a  continuous  cylinder  (shown  in  the  cross  section 
as  a  ring,  Fig.  30). 

45.  Strengthening  cells.  There  are  several  kinds  of  cells 
which  give  either  toughness,  stiffness  (Sect.  46),  or  both  of 
these  qualities  to  the  parts  of  the  plant  body 
where  they  occur.  Only  four  of  these  kinds 
need  be  mentioned  in  this  place.  The  two 
shown  in  Fig.  32  are  commonly  found  in  the 
cortex  of  dicotyledons.  Collenchyma  cells  (A) 
are  like  the  thin-walled  cells  of  the  pith,  but 
are  reenf  orced  at  the 
angles,  just  as  some 
packing  boxes  have 
strips  of  board  nailed 
fast  on  the  inside  of 
the  box  at  the  junc- 
tions of  the  sides. 
Bast  filers  (^)  are 
extremely  slender 
tubes,  with  closed 
and  pointed  ends, 
much  like  a  piece  of 
thermometer  tubing 
drawn  to  a  point  in 
a  gas  flame  and  thus 
closed.  Collenchyma 
gives  moderate  stiff- 
ness to  the  parts  in 
which  it  occurs,  and  is  highly  elastic,  so  that  it  does  not 
hinder  the  growth  of  the  stem  which  it  incloses.  Bast  fibers 
are  flexible  but  very  tough,  and  therefore  enable  the  parts 
of  the  root,  stem,  or  leaf  in  which  they  occur  to  resist  being 
pulled  apart. 


FIG.  32.   A,  collenchymatous  and  other  tissue 

from  stem  of  balsam  (Impatiens) ;  J?,  a  group  of 

hard-bast  fibers 

e,  epidermis ;  c,  Collenchyma ;  i,  intercellular  spaces 

between  large  parenchyma  cells;  a,  cut-off  ends; 

b,  lengthwise  section  of  fibers.  Greatly  magnified. 

A,  after  Strasburger;  B,  after  Tschirch 


48 


PEACTICAL  BOTANY 


Two  other  kinds  of  cells  which  are  important  in  giving 
strength  to  the  plant  body  are  shown  in  Fig.  33.  Tracheids 
(A)  form  a  considerable  part  of  the  fibro- 
vascular  bundles  and  of  the  wood  cylinders 
of  dicotyledons.  The  slender  thick-walled 
ones,  known  as  fiber  tracheids  (^?),  greatly 
strengthen  those  parts  of  the  plant  in  which 
they  occur.  There  is  considerable  difference 
between  wood  fibers  proper  and  tracheids  in 
regard  to  the  tissues  with  which  they  are 
generally  associated,  but  the  fibers  do  not 
differ  much  in  form  from  the  most  slender 
tracheids.  Generally,  however,  tracheids  are 
a  good  deal  stouter  than  wood  fibers,  they 
have  rounded  ends,  and  they  show  spiral  or 
ladder-like  markings  or  oval  or  nearly  circular 
pits  on  their  sides.  Both  wood  fibers  and  thick- 
ened tracheids  serve  to  stiffen  and  toughen 
the  parts  of  the  plants  in  which  they  occur. 

46.  Mechanical  arrangement  of  strength- 
ening materials.  Most  people  know,  in  a 
general  way,  that  a  metal  tube  is  stronger 
than  a  solid  rod  of  the  metal,  of  the  same 
weight  per  foot  of  length.  So,  too,  a  T-rail 
for  steam  or  street  cars,  or  an  I-shaped  girder 
for  bridge  or  other  construction,  is  much 
stiff  er  than  one  of  simple  rectangular  section 
like  an  ordinary  plank. 

In  many  plants  the  stems  and  leaves  show 
great  economy  of  stiffening  material,  having 
the  portions  of  rigid  tissue  so  disposed  as  to 
act  in  the  most  advantageous  way.  Many 
dicotyledons  and  great  numbers  of  mono- 
cotyledons, especially  the  grasses,  have  hol- 
low, nearly  cylindrical  stems.  Sometimes  the 
main  stem  is  not  entirely  hollow,  but  portions 


FIG.  33.  ^tracheid; 

B,  fiber  tracheid  of 

oak  wood 


Magnified  about  125 

diameters.   After  G. 

Mtiller 


THE  STEM  AND  THE  LEAF         49 

of  it  are,  as  in  the  case  of  the  hollow  flower  stalk  of  the  garden 
rhubarb  and  the  dandelion.  More  frequently  the  stem  is  not 
hollow,  but  a  large  mass  of  very  light  spongy  pith  occupies 
the  interior,  as  in  corn,  young  twigs  of  elder  (Fig.  34,  A)  and 
sumach,  and  in  the  entire  stem  of  the  sunflower. 

The  stiffness  of  the  young  stem  may  be  due  almost  wholly 
to  collenchyma,  as  in  the  balsam  (Fig.  32)  and  the  elder 
(Fig.  34,  ^4),  or  it  may  depend  largely  on  the  presence  of 
wood  fibers  and  tracheids  in  the  bundles,  as  in  the  sunflower 
(Fig.  30).  Sometimes  collenchyma  and  fibers  cooperate,  as 
shown  in  the  flower  stalk  of  Eryngium  (Fig.  34,  B).  In  the 


coll 


.  j  >w-i;«re?f.-.?5ViV-    -n 

FIG.  34.  Arrangement  of  strengthening  tissue  A,  J5,  in  stems;  (7,  in  the  root 

A,  cross  section  of  a  young  elder  twig;  B,  cross  section  of  flower  stalk  of  Eryn- 

gium ;  C,  cross  section  of  a  small  root ;  coll,  collenchyma ;  cort,  brittle  cortex ; 

cyl,  tough  central  cylinder ;  /,  fibrous  cylinder  around  a  central  hollow  portion ; 

p,  pith;  w,  woody  bundles  surrounding  the  pith.   After  Strasburger 

case  of  dicotyledonous  trees  the  stiffness  of  the  trunk,  resisting 
the  severest  storms,  is  mainly  due  to  the  immense  number  of 
tracheids  and  fibers  in  the  wood  of  the  annual  cylinders. 

The  stems  of  woody  climbers  need  to  be  at  once  tough  and 
flexible.  Many  such  vines  have,  while  young,  the  structure 
shown  in  the  cross  section  of  Dutchman's-pipe  (Fig.  29),  with 
the  bundles  arranged  in  a  discontinuous  series  around  the 
central  pith  and  not  united  into  a  cylinder.  This  makes  the 
stem  flexible  in  the  same  way  that  a  wire  cable  is  more  flex- 
ible than  a  solid  metal  rod. 

Roots  (except  prop  roots)  do  not  need  to  possess  much  stiff- 
ness ;  it  is  necessary  for  them  to  be  tough  to  resist  lengthwise 


50 


PRACTICAL  BOTANY 


--  m 


pulls,  but  laterally  they  are  supported  by  the  earth.  Accordingly 
it  is  usual  to  find  young  roots  with  a  fibrous  central  cylinder  of 

comparatively  small  di- 
ameter, surrounded  by  a 
coating  of  much  weaker 
tissue  (Fig.  34,  (7). 

47.  Limited  thicken- 
ing of  annual  stems.  In 
stems  of  large  dicoty- 
ledons which  die  to  the 
ground  every  year,  such 
as  sunflowers,  iron  weeds, 
hemp,  giant  ragweed,  and 
so  on,  growth  in  thick- 
ness goes  on  throughout 
the  summer.  The  outer 
cells  of  the  cambium  con- 
tinually split  up,  by  the 
formation  of  tangential 
partitions  (parallel  to 
the  bark),  and  so  form 
new  layers  of  bark.  The 
inner  cells  of  the  cam- 
bium, in  a  similar  way 
and  to  a  still  greater 
extent,  form  new  wood, 
and  thus  the  stem  goes 
FIG.  36.  Cross  section  of  a  stick  of  oak  wood  on  increasing  in  thick 

m,  medullary  rays,  running  from  bark  to  pith ;  ness-    But  m  sucn  plants 

r,  "annual   rings";    6,  boundaries  between  as  those  just  mentioned 

"  rings,"  porous  from  presence  of  many  ducts ;  .  •>            . .    . ,         /•    ,  i 

t,  interior  fibrous  layers  of  dead  bark ;  pi,  hard  the  activity  of  the  cam- 

plates  of  dead  bark,  splitting  away  from  each  bium  is  strictly  limited. 

other  but  attached  to  bark  beneath.  Reduced  Af ^   ^   ^   giyen   ^ 

to  a  certain  amount  of  new  tissue,  growth  stops  and  the  stem 
dies  down  to  the  ground.  The  death  of  annual  stems  in  the 
autumn  is  often  thoughtlessly  supposed  to  be  due  to  the 


THE  STEM  AND  THE  LEAF  51 

arrival  of  cold  weather,  but  it  occurs  just  as  certainly,  and 
often  after  a  briefer  period  of  growth,  in  regions  where  there 
is  no  cold  winter. 

48.  Annual  thickening.  In  stems  such  as  those  of  dicotyle- 
donous trees  and  the  trees  of  the  Pine  family  and  other  cone 
bearers,  which  live  for  many  years,  the  cambium  forms  a  new 
layer  of  bark  and  of  wood  every  year.1  These  annual  layers  are 
usually  more  noticeable  in  the  wood  than  in  the  bark,  because 
the  wood  cylinders  thus  formed  remain  closely  joined  together 
(Fig.  35).  The  newer  lighter-colored  portions  of  the  wood  are 
known  as  sapwood,  and  the  older  portions,  often  darkened  by 
the  deposit  of  coloring  matter,  are  known  as  heartwood.  Not 
infrequently  the  heartwood  decays  and  leaves  the  tree  hollow. 

(1)  How  old  is  the  stick  of  wood  shown  in  Fig.  35  ?  (2) 
Did  it  grow  equally  fast  during  each  year  of  its  life  ?  Dis- 
cuss this  question.  (3)  Why  is  the  name  "  annual  rings  "  not 
an  accurate  one  ?  What  are  they  really  ?  (4)  Is  each  year's 
growth  uniform  all  round  the  stem?  (5)  Had  this  stem  any 
branches  in  the  portion  shown  by  the  section  ?  How  could 
the  age  of  the  stem,  at  the  time  when  a  branch  began,  be 
known  (Fig.  37)? 

The  hardwood  trees  show  great  differences  in  the  rate  at 
which  their  trunks  increase  in  thickness.  Poplars,  bass  woods, 
willows,  or  red  oaks,  growing  in  good  soil  and  unshaded,  may 
for  forty  or  fifty  years  form  annual  rings  as  much  as  three 
eighths  of  an  inch  thick.  But  old  beeches  and  sugar  maples 
in  the  forest,  after  they  have  passed  the  hundred-year  limit, 
often  grow  not  more  than  about  one  sixteenth  of  an  inch  per 
year.  When  very  old,  though  still  sound,  they  may  grow  only 
about  one  twenty-fifth  of  an  inch  per  year. 

Two  of  the  most  important  of  our  coniferous  or  needle- 
leaved  timber  trees  are  the  white  pine  and  the  long-leaf 
pine.  A  white-pine  tree,  overtopping  most  of  its  fellows  in 
the  forest,  is,  on  the  average,  at  ten  years  0.9  inch  in  diameter, 

1  In  the  tropical  regions,  where  there  is  no  marked  change  of  seasons,  the 
wood  often  grows  rather  evenly  all  the  year  round. 


52 


PRACTICAL  BOTANY 


at  one  hundred  years  17.2  inches,  and  at  two  hundred  years  31 
inches.   The  average  thickness  of  the  "  annual  rings  "  during 

the  life  of  the  tree  throughout 
its  second  century  is  therefore 
about  one  fourteenth  of  an 
inch.  In  the  Southern  long- 
leaf  pine,  growth  is  slower. 
The  increase  in  thickness  of  a 
tree  two  hundred  and  twenty 
years  old  and  17|  inches  in 
diameter  was  only  one  inch 
during  the  last  forty  years, 
—  or  one  fortieth  of  an  inch 
per  year. 

In  successful  white-pine 
trees  (that  is,  the  taller  and 
only  slightly  shaded  ones  of 
a  forest)  the  total  amount  of 
wood  formed  in  the  trunk 
per  year  is,  at  fifty  years, 
about  one  fourth  of  a  cubic 
foot,  at  sixty  to  seventy  years 
one  cubic  foot,  at  one  hun- 
dred years  one  and  one  half 
cubic  feet.1 

49  o  Origin  of  branches.  The 
branches  of  dicotyledons  be- 
gin as  little  elevations  or 


FIG.  36.  Diagrammatic  section  through 

the  growing  tip  of  a  dicotyledonous 

shoot,  showing  origin  of  branches 

g,  the  growing  tip  of  the  shoot ;  I,  leaves, 
those  at  the  upper  part  of  the  shoot  the 
youngest;  6j,  62,  63,  64,  branches  of 
various  ages,  arising  in  the  axils  of  the 
leaves.  Note  that  only  the  older  leaves 
and  branches  have  fibrovascular  bundles, 
connecting  with  those  of  the  main  portion 
of  the  shoot  (all  deeply  shaded  in  the 
diagram) .  After  Luerssen 


rounded  outgrowths  from  the 
axis  of  the  leaf  bud,  which  often  terminates  the  stem.2  The 
extreme  tip  of  the  stem  is  the  growing  point  (</,  Fig.  36).  This 
and  much  of  the  neighboring  region  is  made  up  of  cells  which 

1  See  "The  White  Pine,"  Bulletin^  Division  of  Forestry,  U.  S.  Dept.  Agr. 

2  Buds  are  treated  more  in  detail  in  Chapter  VI,  but  it  seems  best  to  say 
a  few  words  in  this  place  about  the  relation  of  the  beginning  branch  to  the 
axis  from  which  it  grows. 


THE  STEM  AND  THE  LEAF 


53 


are  rapidly  dividing  to  form  new  ones,  or,  if  not  dividing,  will 
begin  to  do  so  whenever  they  are  placed  under  favorable 
conditions.  Just  back  of  the  growing  point  appear  little 
protuberances  (I)  which  are  to  develop  into  leaves.  Further 
along  on  the  stem,  each  just  forward  of  a  rudimentary  leaf, 
are  still  more  rudimentary  branches  (bv  62,  and  so  on).  In 
their  youngest  condition  neither  leaves  nor  branches  con- 
tain any  fibrovascular  bundles,  but  these  soon  appear,  as 
shown  by  the  heavily  shaded  areas  in  the  figure.  Once 
equipped  with  bundles  for  the  transportation  of  water  and 
food  materials,  the  growth  of  the  young  branch  into  a  stem 
like  that  from  which  it  sprang,  with  bark, 
wood,  and  pith  of  its  own,  is  comparatively 
rapid.  Branches  of  trees,  being  structur- 
ally of  the  same  nature  as  the  stem,  form 
"  annual  rings,"  just  as  the  main  trunk 
does.  The  wood  of  the  branch  cuts  across 
the  "  annual  rings  "  of  the  trunk  and  forms 
a  knot  (Fig.  37).1 

50.  Internal  structure  of  the  monocoty- 
ledonous  stem.  In  the  very  young  mono- 
cotyledonous  stem  of  seedlings  the  fibro- 
vascular bundles  are  constructed  like  those 
of  dicotyledons,  with  the  wood  elements 
on  the  one  side  and  the  cortical  elements  on 
the  other,  as  in  Fig.  29.  But  in  the  full- 
grown  stems  of  most  monocotyledons  the 

bundles  have  their  vessels  and  other  wood    F'G'37:  Formation  of 
,  ,    .  .    ,_  a  knot  in  a  tree  trunk 

elements    arranged   in   a  hollow  cylinder 

.      ,      .          ,,  *   xt      i         11          ••  .  i       -ff,  cut-off  end  of  stick, 

inclosing    that    part    Of    the    bundle    which     showing  annual  rings  • 


K,    knot,    formed    by 
growth  of  a  branch 


corresponds  to  the  portion  shown  outside 

of  the  cambium  ring  in  Fig.  29.    In  the 

adult  monocotyledonous  stem  (when  it  is  solid)  the  bundles 

occur  scattered  all  through  the  pith,  as  shown  in  a  section  of 

1  Knots  may  also  be  produced  by  injuries,  but  most  of  those  found  in 
ordinary  lumber  were  caused  by  branches. 


54 


PRACTICAL  BOTANY 


asparagus  or  corn  stem  (Fig.  38).    No  such  complicated  bark 
as  that  of  woody  dicotyledons  is  found  in  monocotyledons. 

51.  Growth  in  thickness  of  the  monocotyledonous  stem.  The 
very  young  stem  of  monocotyledons  may  for  a  time  increase 
considerably  in  diameter  by  the  formation  within  it  of  new 
bundles.  But  in  monocotyledons  all  the  cambium  becomes 


FIG.  38.  Cross  section  of  a  corn  stem  (monocotyledonous) 

c,  cortex ;  &',  small  fibro vascular  bundles  near  the  cortex ;  6,  large  bundles  in  the 
interior  of  the  stem ;  p,  pith-like  material  between  bundles.  About  one  and  one- 
half  times  natural  size 

changed  into  other  tissues,  so  that  none  is  left  (as  it  is  in 
dicotyledons)  to  develop  new  tissue.  In  monocotyledons  the 
bundles  are  said  to  be  closed,  while  those  of  dicotyledons  in 
which  active  cambium  remains  are  said  to  be  open.  Most 
monocotyledonous  trees,  such  as  the  palms,  cannot  form  an- 
nual rings  of  wood.  A  few  tree-like  monocotyledons  have 
trunks  which  continue  for  many  years  to  increase  in  thickness, 
but  the  thickening  of  the  trunk  takes  place  in  a  manner  wholly 


THE  STEM  AND  THE  LEAF 


55 


different  from  that  of  dicotyledons.    Many  monocotyledons, 
such  as  the  rattans,  are  remarkable  for  the  extraordinary  length 

and  slenderness  of  their  stems, 
which  often  scramble  for  hun- 
dreds of  feet  over  the  tropical 
forest. 

52.  Arrangement  of  leaves 
upon  the  stem.  A  glance  at  any 
leafy  twig  usually  suffices  to 
show  that  the  leaves  do  not 
spring  from  it  haphazard  but 
are  definitely  arranged.  The 

commonest    methods    of    leaf 

L  39.  Top  view  of  vertical  shoot 

of  "  syringa  "  (Philadelphus) 


arrangement  are  the  opposite 
plan,  in  which  the  leaves  spring 
from  the  nodes  in  pairs  (Figs. 
39  and 40),  as  in  the  maples,  the 
ashes,  the  mints,  and  many  other  plants ;  and  the  alternate  plan, 
in  which  the  leaf  origins  form  a  spiral  about  the  stem,  as  in 


The  leaves  are  arranged  in  pairs  and 
each  pair  overlies  the  spaces  between 
the  pair  below  it.  One  third  natural  size 


FIG.  40.  Top  view  of  a  horizontal  shoot  from  the  same  shrub  shown  in  Fig.  39 

The  leaves  spring  from  the  branch  in  the  same  order  as  do  those  of  the  vertical 
branch,  but  by  a  twisting  of  the  leafstalks  the  blades  are  made  to  lie  nearly  in  a 
horizontal  position  and  thus  secure  abundant  illumination.  One  third  natural  size 


56 


PRACTICAL  BOTANY 


oaks,  corn,  and  most  kinds  of  hard-wood  trees  and  of  herba- 
ceous seed  plants.  There  are  many  varieties  of  spiral  arrange- 
ment, the  simplest 
being  that  of  corn 
and  other  grasses, 
in  which  the  sec- 
ond leaf  is  on  the 
opposite  side  of 
the  stem  from  the 
first,  and  the  third 
is  directly  over  the 
first.  More  com- 
plicated is  the  spi- 
ral of  our  common 
fruit  trees  (Fig. 
41) ;  and  yet  more 
complicated  those 
of  pines  (Chapter 
XVIII),  of  house- 
leeks,  and  of  many 
other  plants. 

53.  Arrangement  on  vertical  stems  in  relation  to  overshadow- 
ing. On  a  vertical  stem  usually  no  leaf  directly  overlies  the  one 
next  beneath  it.  In  the  opposite  arrangement  overshadowing 
is  partially  prevented  by  having  the  leaves  of  each  pair  overlie 
the  spaces  between  the  two  leaves  directly  below  them  (Fig. 
39)".  In  the  various  spiral  arrangements  the  third,  the  sixth, 
or  the  ninth  leaf,  and  so  on,  comes  directly  over  the  first. 

Since  every  foliage  leaf  usually  bears  in  its  axil  a  leaf  bud 
which  may  develop  into  a  branch,  it  follows  that  branch  arrange- 
ment must  depend  upon  and  resemble  leaf  arrangement.1  It  is 
clear,  therefore,  that  the  branches  cannot  usually  directly  over- 
lie each  other.  This  is  plainest  in  the  case  of  opposite  leaves 
and  branches,  but  it  is  fairly  .evident  in  many  other  cases. 

1  Branch  arrangement  is  often  obscured  by  the  dying  of  most  of  the 
branches  (Sect.  60>. 


FIG.  41.  Alternate  arrangement  of  leaves 
An  apple  twig  in  the  autumn 


THE  STEM  AND  THE  LEAF 


57 


54.  Leaf  positions  on  horizontal  stems,  and  overshadowing. 

If  a  rapidly  growing  plant,  as  a  sunflower,  is  bent  over  so  as  to 
lie  flat  on  the  ground,  its  younger  leaves  soon  readjust  them- 
selves to  the  new  position.  Horizontal  branches  of  trees  and 
shrubs  are  very  different  from  vertical  shoots  as  regards  the 
position  of  the  leaf  blades  with  reference  to  the  stem.  Though 
the  opposite  or  the  spiral  arrangement  of  the  leaf  origins  is  the 
same,  a  twisting  of  the  stem,  or  a  lengthening,  or  twisting,  or 


FIG.  42.  Rosettes  of  evening  primrose 

Two  species  are  shown :  CEnothera  rhombifolia  on  the  left,  and  (E.  biennis,  a  very 
widely  distributed  species,  on  the  right.  Photograph  by  W.  J.  G.  Land 

other  change  of  position  of  the  leafstalks  usually  occurs.  This 
comes  about  in  such  a  manner  as  to  put  the  leaves  in  a  favor- 
able position  to  receive  the  sunlight  (Fig.  40).  Prostrate  stems, 
like  those  of  pumpkins,  squashes,  cucumbers,  poison  ivy, 
English  ivy,  and  a  host  of  others,  when  lying  on  the  ground, 
arrange  their  leaves  much  as  do  horizontal  branches  of  trees. 
Trees  that  have  fallen  in  such  a  way  as  to  leave  the  roots  in  the 
soil  may  have  one  or  more  branches  assume  the  form  of  a  tree. 


58 


PRACTICAL  BOTANY 


55.  Leaves  of  apparently  stemless  plants.  Many  plants  have 
a  stem  so  short  that  they  are  commonly  spoken  of  as  stemless. 
Most  of  these  are  perennials,  such  as  the  Iceland  poppy,  the 
common  plantain,  the  true  primroses  (Primula),  and  the  dan- 
delion. There  are  also  numerous  biennials,  such  as  the  parsnip, 

the  carrot,  some 
species  of  wild  let- 
tuce, many  evening- 
primroses  (  (Eno- 
thera),  and  other 
plants,  which  form 
a  tuft  of  leaves  close 
to  the  ground  the 
first  year  and  then 
send  up  a  leafy 
stem  which  flowers 
and  fruits  the  sec- 
ond year.  Such  a 


FIG.  43.  Wild  ginger,  an  apparently  stemless  plant 

A,  the  entire  plant,  with  running  rootstock ;  By  top  view  of  flower ;  (7,  lengthwise 
section  of  flower ;  I,  limb  of  calyx ;  o,  ovary.  Reduced 

tuft  of  leaves  as  that  of  the  dandelion  or  the  evening  primrose 
(Fig.  42)  is  called  a  rosette,  and  plants  in  which  the  appar- 
ently stemless  condition,  with  a  cluster  of  radiating  leaves,  is 
permanent  are  known  as  rosette  plants.  Many  of  these  are 
natives  of  alpine  regions,  and  some,  such  as  the  century  plant 
(Agave,  Fig.  62),  are  found  in  hot,  dry  climates.  Quite  generally 
the  shape  of  the  leaves  in  rosette  plants  secures  economy  of 


THE  STEM  AND  THE  LEAF 


59 


light,  as  they  are  either  narrowed  at  the  base  or  borne  on  long 
leafstalks,  so  that  they  do  not  overlap  and  shade  each  other  at 
the  bases.  The  leaves  of  the  century  plant  are  broad  at  the  base, 


FIG.  44.  Leaf  mosaic  of  a  begonia 
The  leaves  are  so  disposed  that  little  shading  of  one  leaf  by  another  occurs 

but  this  portion  is  pale  and  much  thickened  and  does  hardly 
any  photosynthetic  work,  serving  rather  as  a  storehouse  for 
plant  food.  At  flowering  time  this  food  is  removed,  the  leaves 
droop,  and  after  the  seeds  are  ripe  the  leaves  die  (Fig.  63). 


FIG.  45.  Mosaic  formed  by  leaves  of  unequal  size 
Top  view  of  a  branch  of  deadly  nightshade.  After  Kerner 

56.  Leaf  mosaics.  Any  combination  of  leaves,  whether 
found  in  rosette  plants  or  on  longer  stems,  in  which  the  space 
is  very  fully  occupied  by  leaves,  with  few  spaces  horizontally 
between  them,  is  called  a  leaf  mosaic  (Figs.  44  and  45).  Walls 


60 


PEACTICAL  BOTANY 


covered  with  Japanese  ivy  furnish  beautiful  examples  of  leaf 
mosaics  on  a  large  scale,  and  many  of  our  common  house  plants 
illustrate  the  same  phenomenon.  In  any  leaf  mosaic  many 
of  the  leaves  occupy  a  very  different  position  from  that  which 
they  would  have  if  borne  on  a  vertical  stem. 


FIG.  46.  Poison  ivy,  a  root  climber 
Reduced 

57.  Obtaining  better  illumination 
by  climbing.  While  the  "stemless" 
plants  and  low  mosaic  formers  uti- 
lize light  very  advantageously  by 
the  disposition  of  their  leaves,  many 
plants  get  an  increased  light  sup- 
ply by  climbing.  On  account  of  the 
great  height  and  dense  growth  of 
tropical  forests,  climbing  plants  or  lianas  reach  their  greatest 
development  in  those  regions,  often  running  hundreds  of  feet 
to  emerge  at  last  into  the  blazing  sunlight  above  the  tree  tops. 


FIG.  47.  Twining  stem  of  hop 


THE  STEM  AND  THE  LEAF 


61 


Climbers  are,  however,  quite  generally  distributed,  and  many 
are  familiar  plants  of  our  own  flora.  They  may  be  roughly 
classed  into  (1)  scramblers,  (2)  root  climbers,  (3)  twiners, 
and  (4)  tendril  climbers. 

Scramblers  sprawl  among  and  over  the  tops  of  bushes  and 
thickets.  Examples  are  some  kinds  of  asparagus,  our  common 
climbing  rose,  and  cleavers  (Gralium  Aparine). 


FIG.  48.  Woodbine  or  Virginia  creeper,  a  tendril  climber 
Reduced 

Twiners  raise  themselves  by  winding  the  stem  about  any  slen- 
der upright  support  that  offers  itself.  Well-known  examples 
are  pole  beans,  morning-glories,  and  the  hop.  The  details  of  the 
process  by  which  twiners  wind  themselves  about  a  supporting 
object  cannot  be  very  briefly  stated.  If  carefully  watched, 
the  growing  tip  of  the  shoot  will  often  be  found  to  describe 
revolving  movements  like  those  of  the  hands  of  a  watch.  When 
the  movement  is  arrested  by  contact  of  the  shoot  with  an  ob- 
ject not  too  large  for  the  climber  to  twine  about,  the  resistance 
which  the  young  moving  stem  encounters  causes  it  to  wind 
permanently  around  the  resisting  object  (Fig.  47).  Usually 
the  direction  of  the  coils  for  any  given  plant  is  the  same. 


62  PRACTICAL  BOTANY 

Tendril  climbers  attach  themselves  to  the  stems  or  branches 
of  other  plants  or  to  inanimate  objects  by  means  of  special, 
slender,  thread-shaped,  leafless  organs  called  tendrils.  These 
are  modified  leaves  or  parts  of  a  leaf,  as  in  the  pea  (Fig.  306)  ; 
or  modified  branches,  as  in  the  grape,  the  Virginia  creeper 
(Fig.  48),  and  the  passion  flower.  When  a  living  and  active 
tendril  comes  into  contact  with  a  support,  this  contact  causes 
growth  to  take  place  more  rapidly  on  the  exterior  side  of  the 


FIG.  49.  A  tropical  Smilax,  a  tendril  climber 

a,  tendril  coiled  about  a  portion  of  the  stem ;  I,  tendril  coiled  about  a  leafstalk ; 
br,  a  young  branch ;  t,  young  unattached  tendrils 

tendril  (that  side  which  does  not  touch  the  foreign  object), 
and  thus  the  tendril  is  made  to  coil  about  the  support.  The 
sensitiveness  of  some  tendrils  is  almost  inconceivably  great. 
Those  of  the  star,  wild,  or  bur  cucumber  (Sicyos)  are  stimu- 
lated to  curve  by  a  moving  weight  of  -j  o-oViJo"  °^  a  gram>  or 
one  eighth  of  the  smallest  amount  which  can  be  perceived 
by  the  most  sensitive  part  of  the  human  skin  (the  face). 
After  a  tendril  has  become  attached  the  free  portions  are  also 
thrown  into  coils  and  thus  the  plant  is  drawn  closer  to  the 
support.  As  a  result  of  its  attachment  the  tendril  becomes 
stronger  and  often  considerably  thicker.  In  some  plants, 
as  the  "Virginia  creeper,  the  tendrils  are  enabled  to  fasten 


FIG.  60.  An  English  ivy  (Hedera)  grown  in  front  of  a  south  window 

WW,  the  line  of  the  window  casing ;  all  to  the  right  of  this  is  unlighted  wall.   The 
tips  of  the  shoots  (f)  avoid  the  light ;  the  young  leaves  (I)  have  assumed  no  defi- 
nite position ;  the  mature  leaves  are  nearly  at  right  angles  to  the  light  coming 
from  the  direction  of  the  arrow ;  r,  aerial  roots 
63 


64 


PEACTICAL  BOTANY 


themselves  to  flat  surfaces,  as  of  stones  or  bark,  by  developing 
disks  which  act  as  suckers.  These  may  stick  so  fast  to  the  sup- 
porting surface 
that  the  tendril 
can  be  broken 
without  tearing 
them  away. 

58.  Leaf  posi- 
tions avoiding  ex- 
cessive illumina- 
tion. While  the 
leaves  of  plants 

growing   in    the 
FIG.  51.  Nearly  vertical  leaves  °,     ,      °f  „ 

of  the  olive  shade  of ten  suf- 

fer  from  lack  of 

sunlight  and  are  usually  so  arranged  as  to  utilize  most  fully 
what  light  there  is  (Fig.  50),  it  is  possible  for  leaves  in  exposed 
situations  to  have  too  much  light.  It  seems  certain  that  the  most 
powerful  sunlight  may  injure  the  chloroplasts  and  therefore 
cripple  the  power  of  the  leaf  to  do  its  work  of  photosynthesis. 
Compass  plants,  such  as  the  common  prairie  species  (>SVZ- 
phium)  and  the  prickly  lettuce,  have  leaves  somewhat  erect, 
with  edges  directed  nearly 
north  and  south,  thus  se- 
curing good  illumination 
during  the  cooler  morning 
and  evening  hours,  but  pre- 
senting the  leaves  nearly 
edgewise  to  the  sun  at  noon. 
Many  other  plants  maintain 
some  or  all  of  their  leaves 
in  a  nearly  vertical  posi- 
tion, but  with  the  edges 
not  directed  north  and  south.  In  the  olive  (Fig.  51)  many 
leaves  point  nearly  upward,  while  in  the  commonest  species 
of  Eucalyptus  the  leaves  hang  vertically  downward. 


FIG.  52.  A  leaf  of  red  clover 

At  the  left,  leaf  by  day ;  at  the  right,  the 
same  leaf  at  night.   Natural  size 


THE  STEM  AND  THE  LEAF 


65 


In  a  great  number  of  trees  the  young  leaves  from  recently 
opened  buds  stand  erect  or  hang  straight  down.  In  one 
tropical  species1  it  is  estimated  that  these  young  drooping 
leaves  do  not  get  more  than  -5^  as  intense  illumination  as  is 
received  by  the  most  exposed  of  the  mature 
leaves. 

59.  Daily  movements  of  leaves.  It  is  com- 
mon to  find  leaves  assuming  different  posi- 
tions during  different  portions  of  the  day,  or 
even  whenever  (as  from  the  long  continuance 
of  clouds  over  the  sky)  the  intensity  of  the 
sunlight  is  much  altered.  These  daily  changes 
of  position  are  particularly  frequent  in  plants 
of  the  Pea  family,  and  many  of  these  have  a 
special  cushion-like  organ,  the  pulvinus,  at 
the  base  of  the  leafstalks  or  of  the  leaflets, 
which  produces  the  movements.  Sometimes, 
as  in  Fig.  52,  there  are  only  two  principal 
positions  assumed  during  the  entire  twenty- 
four  hours,  one  for  the  day,  the  other  for  the 
night.  In  other  cases  there  are  at  least  three 
well-defined  positions,  as  in  the  case  of  the 
black  locust  leaf.  In  this  the  leaflets  droop 
at  night,  remain  nearly  horizontal  in  ordinary 
daylight,  and  stand  erect  in  full  sunlight. 

It  is  certain  that  the  plant  gains  some  ad- 
vantages from  the  change  from  horizontally 
placed  to  vertically  placed  leaflets,  and  the 
reverse.  The  horizontal  position  is  (as  already 
stated)  favorable  for  photosynthesis  in  mod- 
erate light,  and  the  vertical  position  hinders  undue  absorp- 
tion of  intense  sunlight  by  the  chloroplasts.  What  benefit 
the  plant  gets  from  the  assumption  of  the  night  position  by 
the  leaves,  and  of  how  much  importance  this  is,  are  questions 
as  yet  unsettled. 

1  Amherstia  nobilis,  from  Burma. 


FIG.  53.  The  purple 
wood  sorrel,  with 
the  leaves  in  the 
nocturnal  position 

One  third  natural 
size 


66 


PEACTICAL  BOTANY 


60.  Self-pruning  of  leaves  and  twigs.  Many  trees  and  shrubs 
begin  to  shed  some  of  their  leaves  even  in  the  spring,  very 
soon  after  the  leaves  are  well  grown.  Examples  of  this  are 
the  lilacs,  the  syringa  (Philadelphus~),  the  cottonwood,  the 
horse-chestnut,  the  box  elder,  and  some  lindens.  Still  more 
common  is  the  loss  of  leaves  during  the  summer,  which  may 
amount  to  30  per  cent  of  the  total  number  of  leaves.  This 
leaf  fall,  coming  long  before  the  leaves  are  cast  off  in  the  autumn 
as  a  preparation  for  winter,  affects  mostly  the  leaves  inside 

the  crown  of  the 
tree,  which  have 
such  scanty  light 
that  they  can- 
not accomplish 
much  photosyn- 
thesis. 

Leaves,  twigs, 
and  even  larger 
branches  which 
are  not  getting 
an  adequate  sup- 
ply of  light  or  of 
water  are  pruned 
away  by  the  tree. 
Were  it  not  for 
this,  the  dense  growth  in  the  interior  of  the  tree  top  and 
along  the  trunk  would  soon  render  further  branching  me- 
chanically impossible.  What  one  sees  on  looking  up  along 
the  trunk  into  the  top  of  a  large  tree  is  mainly  dead  or  dying 
branches,  with  few  leaves.  It  is  this  self -pruning  and  pruning 
by  neighboring  trees  which  makes  the  straight  trunks,  free 
from  knots  and  most  valuable  for  timber,  in  trees  grown  in 
woodlands,  where  they  stand  moderately  close  together.  In 
some  instances,  as  the  so-called  snap  willows,  the  cotton- 
wood,  and  the  large-toothed  aspen,  live  twigs  fall  very  freely 
from  the  tree  during  wind  or  snowstorms,  or  when  it  is  loaded 


FIG.  54.  A  leaf  of  acacia 

A,  as  seen  by  day ;  B,  the  same  leaf  at  night.  After 
Darwin 


THE  STEM  AND  THE  LEAF 


67 


with  sleet  (Fig.  28).  These  may  be  blown  over  crusted  snow 
or  floated  along  by  brooks  or  rivers  near  which  the  trees 
grow,  and  doubtless  often  lodge  in  spots  where  they  take  root 
and  grow  into  new  trees. 

61.  Aerial,  floating,  and  submerged  leaves  of  water  plants. 
Many  plants  which  grow  rooted  under  water  have  only  aerial 
leaves.  To  this  class  belong  many  arrowheads,  the  cat-tails, 


FIG.  55.  Victoria  regia  and  other  tropical  and  sub-tropical  water  lilies  at 
the  nurseries  of  Henry  A.  Dreer,  Philadelphia 

The  Victorias  have  the  largest  known  floating  leaves,  sometimes  six  feet  in 
diameter  and,  like  rafts,  capable  of  supporting  large  water  birds 

wild  rice,  pickerel  weeds,  and  other  familiar  species.  A  few 
common  plants  like  the  pond  lilies  and  Victorias  have  floating 
leaves  only  (Fig.  55).  Some  water  crowfoots  and  pondweeds 
have  all  their  leaves  submerged,  while  other  species  of  these 
plants  and  some  arrowheads  have  part  of  their  leaves  ex- 
posed to  the  air  and  others  wholly  under  water. 

Submerged  leaves  are  often  made  up  of  many  thread-like 
divisions,    apparently  to    enable  them  to  present   as    much 


68  PRACTICAL  BOTANY 

surface  as  possible  to  the  water,  in  order  that  they  may  ab- 
sorb from  it  the  gases  dissolved  in  it.  Their  shape  somewhat 
resembles  that  of  the  gills  of  fishes,  and  the  thread-like  divi- 
sions of  the  leaf  and  the  gill  both  have  to  do  the  work  of 
absorbing  dissolved  gases. 

62.  Leaves  in  relation  to  water  supply.  The  form  and  size 
of  leaves  are  frequently  dependent  on  the  water  supply  which 
the  plant  receives.  In  many  plants  which  grow  in  moist  soil 
or  even  in  swamps  the  leaves  are  large  and  often  entire,  as 
in  the  Cypripedium,  skunk  cabbage,  white  hellebore,  papaw, 
and  the  magnolias. 

In  very  dry  soils  or  where  the  rainfall  is  scanty  or  lacking 
during  a  considerable  part  of  the  warm  months,  there  occur 
many  plants  whose  leaf  surface  is  very  small,  as  in  some  Eu- 
phorbias, aloes,  and  heaths  (Erica)  ;  or  is  even  practically 
wanting,  as  in  most  cacti  (Fig.  65).  This  reduced  leaf 
surface  evidently  fits  plants  admirably  to  resist  death  from 
excessive  transpiration  during  droughts. 

When  the  soil  temperature  is  nearly  at  the  freezing  point 
most  plants  are  unable  to  absorb  much  water  by  their  roots. 
It  is  probably  mainly  due  to  this  fact  that  our  ordinary  winter 
deciduous  trees  owe  their  habit  of  shedding  the  leaves  at  the 
approach  of  winter.  If  their  actively  transpiring  leaves  were 
to  remain  at  work  while  the  ground  was  almost  or  quite  frozen, 
the  tree  would  suffer  a  fatal  loss  of  water.  Winter  deciduous- 
ness  is  not  a  perfectly  definite  phenomenon,  always  setting  in 
at  precisely  the  same  season.  For  example,  the  common  Jap- 
anese honeysuckle,  which  is  deciduous  in  the  late  autumn  or 
early  winter  in  the  Northeastern  States,  is  almost  or  quite  ever- 
green in  the  South,  and  the  trumpet  honeysuckle  is  deciduous 
in.  the  North  and  perfectly  evergreen  in  the  South.  Such  de- 
ciduous trees  as  the  American  tulip  tree  (Liriodendrori)  and 
the  English  oak  become  irregularly  evergreen  in  the  very 
uniform  climate  of  West  Java ;  that  is,  they  show  in  December 
and  January  (on  separate  boughs)  a  state  of  things  correspond- 
ing to  their  winter,  spring,  and  summer  condition  in  their 


THE  STEM  AND  THE  LEAF 


69 


native  countries.  The  process  of  shedding  the  leaf  is  a  some- 
what complicated  one,  being  brought  about  by  the  formation 
of  a  waterproof  layer  of  tissue  at  the  base  of  the  leafstalk, 


FIG.  56.  An  evergreen  rhododendron,  typical  of  leathery-leaved 
non-deciduous  dicotyledons,  in  very  early  spring 

A  deciduous  rhododendron  (azalea)  is  seen  leafless  in  the  foreground 
Photograph  by  Robert  Cameron 

thus  cutting  the  leaf  off  from  communication  with  the  stem. 
Before  this  is  formed,  the  plant  food  in  the  leaf  has  usually 
been  conveyed  into  other  parts  of  the  plant,  so  that  when  the 
leaf  falls  it  takes  with  it  little  of  value. 


70 


PRACTICAL  BOTANY 


Some  trees  and  many  shrubs  in  countries  like  the  Medi- 
terranean region  and  California,  where  the  hotter  months  are 


B  C 

FIG.  57.  Hairs  which  protect  leaves  from  excessive  loss  of  moisture 

A,  T-shaped  hairs  of  wormwood  ;  B,  silky  hairs  of  Convolvulus;  C,  shield-shaped 
scaly  hairs  of  Elseagnus.   All  considerably  magnified.   After  Kerner 

nearly  rainless,  are  summer-deciduous,  losing  almost  or  quite 
all  of  their  leaves  at  the  beginning  of  summer.  Twigs  in 
this  leafless  summer  condi- 
tion have  been  found  to 
lose  only  about  ^  as  much 
water  in  a  given  time  as 
they  do  when  in  full  leaf. 
63.  Hairs  and  other  cover- 
ings of  the  leaf  surface.  The 
leaves  of  many  kinds  of 
plants  are  covered  with  a 
layer  of  wax  or  of  a  var- 
nish-like material ;  some  are 

coated    with    a    deposit    of     FIG.  58.  Part  of  epidermis  of  geranium 

(Pelargonium),  surface  view 


lime  salts,  and  all  of  these 
substances  appear  to  hin- 
der excessive  loss  of  water 
from  the  leaves.  A  similar 
purpose  is  subserved  by  a 


A,  hairs,  the  one  at  the  left  consisting  of  one 
cell,  the  one  at  the  right  several-celled  and 
bearing  a  gland  at  its  tip ;  e,  stout  cells  of 
the  epidermis,  which  serve  to  support  the 
hair.  Between  the  hairs  a  stoma  is  seen, 
Considerably  magnified 


THE  STEM  AND  THE  LEAF         71 

clothing  of  dry  hairs,  which  often  assume  very  curious  forms 
(Fig.  57).  These  may  completely  cover  one  or  both  surfaces 
of  the  leaf  (usually  the  lower  one).  Such  hair-clad  leaves  are 
very  commonly  found  on  mountain  and  desert  plants  and  on 
those  which  grow  in  regions  with  a  long  and  rainless  summer, 
and  it  has  been  experimentally  proved  that  the  hairs  greatly 
lessen  evaporation  from  the  leaves.  Speaking  of  the  flora  of 
the  summer-dry  Mediterranean  region,  the  distinguished  Aus- 
trian botanist  Kerner  says:  "The  trees  have  foliage  with  gray 
hairs ;  the  low  undergrowth  of  sage  and  various  other  bushes 
and  semi-shrubs  ...  as  well  as  the  perennial  shrubs  and 
herbs  growing  on  sunny  hills  and  mountain  slopes,  are  gray 
or  white,  and  the  preponderance  of  plants  colored  thus  to 
restrict  evaporation  has  a  noticeable  influence  on  the  charac- 
ter of  the  landscape.  He  who  has  only  heard  from  books  of 
the  evergreen  plants  of  the  Greek,  Spanish,  and  Italian  floras, 
feels  at  the  first  sight  of  this  gray  vegetation  that  he  has  been 
in  some  degree  deceived,  and  is  tempted  to  alter  the  expression 
'  evergreen '  into  '  ever  gray.'  " 

Hairs  which  contain  liquid,  like  the  gland-bearing  one  in 
Fig.  58,  do  not  serve  to  prevent  evaporation,  but  are  some- 
times of  much  use  for  other  purposes,  as  in  carnivorous  plants 
(Chapter  XXI). 


CHAPTER  V 


UNDERGROUND  STEMS ;  STORAGE  IN  STEMS  AND  LEAVES ; 
REPRODUCTION 

64.  Characteristics  of  underground  stems.  The  popular  notion 
of  what  a  stem  is,  includes  the  idea  that  it  is  an  aerial  part  of 
the  plant.  It  is  easier  to  recognize  as  roots  such  structures 
as  the  aerial  roots  of  corn  and  of  poison  ivy  than  it  is  to  rec- 
ognize as  stems  the  thickened  underground  portions  of  iris, 
jack-in-the-pulpit,  dragon-root,  trillium,  or  potato.  Frequently, 

like  aerial  stems,  underground 
stems  are  divided  into  nodes 
and  internodes ;   and  many  of 
them  bear  scales  which  repre- 
sent leaves,  and  produce  buds 
in   the    axils    of   these    scales. 
Such  buds  are  well  shown  in 
the  underground  stems  of  some  grasses. 
Dicotyledonous  underground  stems  usu- 
ally have  distinct  bark,  wood,  and  pith, 
while  most  dicotyledonous  roots  do  not 
have  pith,  though  some  do. 


FIG.  59.  A  May-apple  plant,  showing  the  history  of  the  rootstock 

1  is  the  oldest  surviving  portion  of  the  rootstock ;  2  is  a  year  younger ;  3  a  year 
younger  than  2,  and  so  on.  At  each  figure  the  cluster  of  roots  marks  the  position 
of  the  base  of  the  upright  stem  for  that  year,  as  is  shown  at  6.  b,  bud  for  the  new 
year's  growth ;  br,  bract  at  the  base  of  the  present  stem.  One  sixth  natural  size 

72 


UNDERGROUND  AND  AERIAL  STEMS 


73 


Some  of  the  principal  forms  of  underground  stems  have  for 
convenience  been  given  special  names.  The  elongated  forms 
like  that  of  the  May  apple  (Fig.  59),  mints,  couch  grass,  and 
many  other  plants,  and  some  stouter  kinds  like  that  of  trillium 
and  Solomon's-seal  (Fig.  60),  are  known  as  rootstocks  or  rhizomes. 
The  very  short  shoots  with  disk-like  stems  and  a  covering  of 
scales,  familiar  in  some  lilies,  the  hyacinth  (Fig.  61),  and  the 
onion,  are  called  bulbs. 
Much  like  bulbs,  ex- 
cept that  the  stem  is 
more  developed  and 
that  the  scales  are 
almost  lacking,  are  tu- 
bers, like  those  of  the 
Jerusalem  artichoke 
(Fig.  67),  the  potato, 
and  the  crocus.1  The 
potato  is  a  particularly 
good  tuber  for  study, 
as  it  has  well-defined 
nodes  and  internodes ; 
the  buds  ("eyes")  are  arranged  in  a  distinctly  spiral  manner, 
and  are  borne  in  the  axils  of  little  scales  which  represent  leaves, 
and  not  infrequently  the  tuber  is  considerably  branched. 

65.  Aerial  outgrowths  of  underground  stems.  Some  under- 
ground stems  produce  a  leafy  aerial  stem,  while  others  send 
up  leaves  but  have  no  stem  above  ground.  A  good  example 
of  the  former  class  is  the  lily  or  the  Jerusalem  artichoke ;  of 
the  latter,  the  ferns  of  temperate  regions,  many  grasses,  wild 
ginger  (Fig.  43),  and  some  of  the  commonest  violets  (Fig. 
124).  In  any  case  the  aerial  parts  of  herbs,  in  cold  or  tem- 
perate climates,  usually  die  to  the  ground  at  the  beginning 
of  winter.  In  regions  with  a  long,  rainless  summer  they  fre- 
quently die  soon  after  the  end  of  the  spring  rains.  The  buried 

1  Such  very  short  underground  stems  as  that  of  the  jack-in-the-pulpit 
and  the  crocus  are  often  called  corms. 


FIG.  60.  Rootstock  of  Solomon's-seal 

rh,  rhizome  or  rootstock;   6,6',  buds;  r,  roots; 

s,  stem.  The  scar  where  an  old  stem  was  attached 

is  seen  just  above  6" 


74 


PRACTICAL  BOTANY 


part  of  the  plant  body,  with  its  terminal  bud  or  sometimes 
lateral  buds,  is  comparatively  safe  from  extremes  of  cold  or 

dryness,  and  serves 
to  carry  the  life  of 
the  plant  over  from 
one  growing  season 
to  another. 

66.  Water  storage 
in  stems.  All  living 
stems  of  plants  con- 
tain water,  and  in 
the  case  of  plants  ex- 
posed to  long  peri- 
ods of  drought  the 
water  stored  in  the 
stem  may  be  abso- 
lutely necessary  to 
tide  over  the  rainless 
months.  Some  cacti 
and  other  succulent 
desert  plants  con- 
tain enough  water 
to  make  it  possible 
for  men  and  other 
animals  to  drink 
from  them  when  they 
are  cut  open.  The 
amount  of  water 
stored  in  some  desert 
plants  is  sufficient  to 
carry  on  growth  and 


FIG.  61.  Lengthwise  section  through  a  young 
hyacinth  plant 


*t  the  cushion-shaped  stem  at  the  base  of  the  bulb ;     reprO(iuction  for  ten 

6,  the  young  bulb  from  which  the  next  year  s  growth 

would  proceed;  sc,  bulb  scales;  f.s,  flower  stalk,     years  or  more  Wlth- 

Eeduced  out    renewal     from 

outside  sources.    The  trunks  of  certain  South  American  trees 
are  so  swollen  as  to  constitute  something  like  aerial  tubers, 


STOEAGE  IN  STEMS  AND  LEAVES  75 

and  great  numbers  of  desert  plants  have  bulbs  or  rootstocks 
much  exceeding  in  bulk  the  rest  of  the  plant  body,  and  con- 
taining large  quantities  of  water,  protected  from  evaporation 
by  heavy  exterior  layers  of  cork. 

67.  Water  storage  in  leaves.  Many  of  the  most  striking 
examples  of  succulent  or  fleshy-leaved  plants  occur  among 
species  which  are  natives  of  dry  countries  or  of  regions  where 
there  are  long  rainless  periods.  The  century  plants  (Agave) 
(Fig.  62),  ice  plants  (MesembryantJiemurn)^  aloes  (Alo'e),  and 
Echeveria  are  good  instances  of  this  kind  of  leaf.  The  leaves 
are  sometimes  cylindrical  or  prismatic,  thus  offering  little 
surface  for  evaporation,  and  contain  great  quantities  of  water 
in  the  form  of  a  thin  mucilage,  not  easily  dried  up.  In  many 
such  leaves  the  water  is  largely  stored  in  special  layers  of  the 
epidermis,  while  in  others  the  water-storage  tissue  is  in  the 
interior  of  the  leaf.  During  droughts  fleshy  leaves  gradually 
lose  their  firmness  and  become  flabby  in  the  same  way  as  the 
leaves  of  the  purslane  do  when  the  plant  is  hoed  up  and  left  on 
the  surface  of  the  ground.  In  tliis  case  the  plant  may  live  for 
weeks  and  then  take  root  and  grow  again  after  the  first  rain. 

Sometimes  plants  which  grow  in  moist  soil  have  leaves  with 
water-storage  layers.  The  oleander,  for  instance,  grows  along 
water  courses  but  is  exposed  for  months  to  very  dry,  hot  air, 
during  the  nearly  rainless  summers  of  the  Mediterranean  region. 
The  common  rubber  plant  (Ficus),  which  in  India  grows  to 
be  an  immense  tree,  is  one  of  the  most  familiar  examples  of 
water  storage  in  the  leaves  of  a  species  growing  in  moist  soil. 
Such  leaves  are  able  to  withstand  the  great  changes  of  tem- 
perature and  moisture  in  the  air  of  the  tropics  during  every 
twenty-four  hours,  the  air  for  two  thirds  of  the  time  being 
almost  saturated  with  moisture,  while  during  the  remaining 
hours  the  moisture  is  relatively  low  and  the  temperature  under 
a  nearly  vertical  sun  extremely  high. 

Plants  with  fleshy  leaves  are  often  found  in  cool,  damp  cli- 
mates, but  they  usually  grow  on  rocks  or  in  other  situations 
where  the  water  supply  is  at  times  nearly  or  quite  cut  off. 


76 


PRACTICAL  BOTANY 


68.  Air  storage  in  stems  and  leaves.  In  many  marsh  and 
water  plants  very  extensive  supplies  of  air  are  stored  in  the 

interior  of  the  roots,  rootstocks, 
the  ordinary  stems,  and  the 
leaves.  This  stored  air  consti- 
tutes what  has  been  well  called 
an  inner  atmosphere,  by  means 
of  which  the  respiration  of  the 
plant  is  much  aided,  especially 
at  times  when  the  whole  plant 
body  is  temporarily  submerged. 
In  those  marsh  or  water  plants 
which  have  the  most  extensively 
developed  air  passages  and  cav- 
ities they  form  a  complex  system 
which  extends  all  the  way  from 
the  stomata  to  the  tips  of  the 
roots.  Often  a  large  part  of  the 
bulk  of  the  plant  body  is  occu- 
pied by  such  air  cavities,  sur- 
rounded by  slight  walls  of  solid 
material.  In  the  leaves  of  Pistia, 
a  floating  aquatic  belonging  to 
the  Arum  family,  71  per  cent  of 
the  volume  is  occupied  by  air 
spaces,  while  in  ordinary  land 
plants  these  spaces  may  occupy 
less  than  7  per  cent  of  the  total 
volume  of  the  leaf. 

An  important  mechanical  use 
is  often  subserved  by  stems  or 
leaves  inflated  with  air,  in  buoy- 
ing up  the  plant,  as  is  well  shown 
by  the  duckweeds,  the  water 
hyacinth  (EicTihomicT),  and  the  water  chestnut  (Trapa).  Many 
seaweeds,  as  the  rockweed,  are  thus  buoyed  up. 


FIG.  62.  A  century  plant,  nearly 
ready  to  blossom 

The  flower  stalk  considerably  devel- 
oped and  the  outer  leaves  beginning 
to  shrivel  and  droop  from  loss  of 
food  transferred  to  the  flower  stalk. 
Photograph  by  G.  D.  Fuller 


STORAGE  IN  STEMS  AND  LEAVES 


77 


69.  Storage  of  food.  Aerial  stems  contain  plant  food,  often 
in  great  quantities.  In  the  trunks  of  trees  this  food  is  present 
in  various  forms,  —  as  starch, 
sugar,  oil,  and  proteins.  Many 
kinds  of  sapwood  turn  deep  blue 
or  black  if  tested  with  iodine  for 
starch  in  the  autumn.  During 
the  winter  much  of  this  starch 
is  often  converted  into  sugar 
or  oil.  The  presence  of  proteins 
in  wood  is  so  general  that  the 
cheaper  grades  of  white  paper, 
largely  made  of  wood  pulp,  at 
once  turn  yellow  on  being  mois- 
tened with  nitric  acid  (protein 
test).  When  thus  tested,  paper 
made  wholly  of  cotton,  or  of 
linen  rags,  shows  little  change. 
The  plant  food  stored  in  wood 
is  most  abundant  in  the  younger 
portions  (sapwood),  and  above 
all  in  the  cambium  layer. 

Underground  stems  often  con- 
tain large  quantities  of  stored 
food,  and  are  thus  useful  in 
tiding  over  the  period  of  the 
year  when  no  food  can  be  made, 
just  as  they  have  already  (Sect. 
66)  been  shown  to  be  of  serv- 
ice in  storing  water.  There  are 
many  shade  plants  —  such  as 
trilliums,  dogtooth  violets  (Fig. 
66),  wild  ginger  (Fig.  43),  May 
apple  (Fig.  59),  and  others  — 
which  leaf  and  blossom  early  in  the  spring  and  do  a  large  part 
of  the  storing  of  food  for  the  next  season  in  their  rootstocks, 


FIG.  63.  The  century  plant  of  the 

preceding  figure  as  it  appeared 

nearly  two  months  later 

The  leaves  have  given  up  their  stored 

food  to  the  flowers  and  flower  stalk 

and  are  now  withered  and  valueless. 

Photograph  by  G.  D.  Fuller 


78  PRACTICAL  BOTANY 

tubers,  or  bulbs,  before  the  trees  under  which  they  grow  are 
in  full  leaf,  so  as  to  shut  out  the  abundant  light  necessary 
for  photosynthesis. 

Fleshy  leaves  often  contain  much  stored  food,  as  in  the 
familiar  century  plant  (Figs.  62  and  63).  This  receives  its 
name  from  the  commonly  received  idea  that  it  must  store  food 
for  a  century  before  it  can  blossom.  In  hot  climates,  however, 
such  as  that  of  Arizona,  near  Tucson,  it  flowers  at  the  age  of 
fifteen  years  or  but  little  more.  By  the  end  of  the  flowering 
season  the  leaves  have  lost  more  than  90  per  cent  of  their 
weight,  which  has  been  expended  in  producing  the  immense 
flowering  shoot.  This  may  reach  a  height  of  over  33  feet  and 
a  weight  of  some  500  pounds.  Its  average  growth  in  height 
during  the  month  of  most  rapid  elongation  has  been  found  to 
be  about  five  and  one  half  inches  a  day.  Not  only  the  plant 
food,  but  also  nearly  all  of  the  water  for  this  rapid  growth  is 
furnished  by  the  leaves. 

70.  Food  for  reserve  stores  brought  from  elsewhere.  In  all 
plants  of  high  organization  the  reserve  food  is  carried  from 
the  cells  in  which  it  was  manufactured  into  other  cells.    In 
plants  with  fleshy  leaves,  like  the  houseleek,  the  century  plant, 
the  common  purslane,  and  many  others,  the  greater  part  of  the 
stored  starch  and  other  nutritive  materials  has   only  been 
carried  from  the  outer  portions  of  the  leaf,  where  photosyn- 
thesis and  other  manufacturing  processes  go  on,  into  the  leaf 
interior.    The  distance  traversed  may  be  only  a  small  fraction 
of  an  inch.    But  in  case  much  of  the  food  is  stored  in  under- 
ground parts  of  the  plant  it  may  have  been  carried  for  long 
distances,  in  large  trees  even  much  more  than  a  hundred  feet. 

71.  Form  in  which  plant  food  is  carried.    As  is  suggested 
in  Sect.  17,  the  first  visible  product  of  photosynthesis  in  most 
plants  is  starch.    This  is  deposited  in  or  about  the  substance 
of  the  chloroplasts,  during  their  exposure  to  daylight,  in  the 
form  of  very  minute  grains.    In  the  course  of  the  night  these 
disappear,  so  that  testing  a  leaf  with  iodine1  shortly  before 

1  This  turns  starch  grains  blue  or  almost  black. 


STORAGE  IN  STEMS  AND  LEAVES 


79 


daylight  usually  gives  no  result.  However,  in  case  the  leaf  is 
cut  off  from  the  stem  before  nightfall,  it  responds  readily  to  the 
iodine  test  for  starch  in  the  morning.  This,  of  course,  shows 
that  the  starch  made  during  the  day  had  no  outlet  and  there- 
fore remained  in  the  leaf  cells  where  it  was  formed.  Very 
generally  starch  carried  away  from  any  part  of  the  plant 
body  to  another  part  is  first  changed 
to  sugar  and  travels  in  the  form  of  a 
very  weak  solution  of  sugar  in  water. 
On  its  arrival  at  the  storage  region 
(as  in  the  case  of  the  potato  plant  at 
the  tuber)  the  dissolved  sugar  is  re- 
converted into  starch  by  the  action  of 
minute  colorless  corpuscles  of  proto- 
plasm known  as  leucoplasts.  The  starch 
grains  deposited  for  storage  (Fig.  64) 
are  many  times  larger  and  show  a  far 
more  definite  structure  than  those 
formed  in  the  chloroplasts  during 
photosynthesis. 

72.  How  plant  food  is  carried;  diffusion.  If  a  little  molasses 
is  poured  into  a  straight-sided  jar  and  water  is  carefully  added, 
a  disk  of  porous  paper  being  first  laid  on  the  surface  of  the 
molasses  to  prevent  instantaneous  mixing,  the  water  will  for 
a  considerable  time  appear  clear  and  colorless.  Only  after 
some  hours  will  the  molasses  rise  and  mingle  much  with  the 
water,  or  the  latter  perceptibly  thin  the  molasses.  This 
process  by  which  two  liquids  in  contact  become  mixed  by 
the  interchange  of  inconceivably  minute  portions  (molecules) 
of  both  liquids  is  called  diffusion.  The  interchange  of  diffusi- 
ble liquids  through  a  membrane  without  visible  pores,  such  as 
an  ordinary  cell  wall,  is  called  osmosis.  Ordinarily  in  osmosis 
the  stronger  flow  is  from  the  less  dense  to  the  denser  liquid. 
In  the  case  of  the  starch-loaded  leaf  (Sect.  71)  it  is  evident 
that,  as  fast  as  the  starch  grains  temporarily  deposited  in 
the  chloroplasts  are  changed  into  sugar,  some  of  the  sugar 


FIG.  64.  Starch  from  root- 
stock  of  Canna.  Magnified 
300  diameters 


80  PEACTICAL  BOTANY 

in  the  denser  cell  sap  thus  produced  will  pass  on  to  the  more 
watery  sap  of  adjacent  cells.  From  these  cells  in  turn  por- 
tions of  sugar  will  pass  on  to  other  more  distant  cells.  In  a 
similar  way,  when  a  potato  tuber  is  planted  and  begins  to 
sprout,  the  sugar  formed  from  the  reserve  starch  in  the  potato 
will  pass  into  the  more  watery  sap  contained  in  the  sprouts. 
This  sap  is  constantly  losing  sugar  that  is  used  as  building 
material  for  the  young  growing  stems  and  leaves,  and  its 
strength  can  be  maintained  only  by  the  addition  of  new  por- 
tions of  sugar  coming  from  the  tuber.1 

73.  Channels  by  which  plant  food  is  carried.  Many  kinds 
of  living  tissue  serve  as  channels  for  the  conveyance  of  food 
from  one  part  of  the  plant  body  to  another.  The  main  route 
for  the  transportation  of  food  in  flowering  plants  is  through 
special  tubular  cells  forming  the  sieve  tubes,  so  called  from  the 
perforated  plates  which  are  found  at  the  ends  or  along  the 
sides  of  the  nearly  cylindrical  cells  of  which  the  tubes  are 
built  up.  These  sieve  tubes  in  dicotyledons  occupy  a  region 
of  the  stem  immediately  outside  of  the  cambium,  as  shown  at 
o  in  Fig.  29.  The  fact  that  most  of  the  plant  food  prepared 
in  the  leaves  is  carried  down  through  the  sieve  layer  of  the 
bark  is  well  shown  by  the  behavior  of  a  willow  cutting  from 
which  a  ring  of  bark  has  been  removed.  If  the  cutting  is 
stood  with  its  lower  end  in  water  but  with  the  girdled  part 
out  of  water,  enough  constructive  material  will  pass  down 
through  the  sieve  layer  to  send  out  roots  from  the  upper  edge 
of  the  ring,  but  few  or  none  will  appear  at  its  lower  edge. 
Water  meantime  is  freely  carried  upward  through  the  sap  wood. 
In  early  times  the  process  of  clearing  woodlands  for  farming 
purposes  was  made  less  laborious  by  girdling  the  trees,  which 
soon  died  and  at  length  fell  and  were  burned.  Would  the  gir- 
dling process  be  more  effective  if  a  good  deal  of  the  sapwood 
were  removed  from  the  ring  as  well  as  the  bark  ?  Explain. 

1  It  is  not  possible  here  to  go  into  details  concerning  the  transportation 
of  other  kinds  of  plant  food  than  starch  and  the  sugars.  That  of  proteins  is 
especially  difficult  to  trace. 


STORAGE  IN  STEMS  AND  LEAVES 


81 


FIG.  65.  Prickly-pear  cactus 


It  seems  certain  that  a  good  deal  of  the  transportation  of 
food  substances  inward  from  the  sieve  tubes  toward  the  cen- 
ter of  the  stem  is  done  by  the  medullary  rays  (Fig.  35,  m). 


82  PEACTICAL  BOTANY 

74.  Stems  as  sources  of  animal  food.  The  life  of  men  and 
of  many  species  of  the  lower  animals  is  largely  sustained  by 
vegetable  food  obtained  from  the  stems  of  plants.    Cane  sugar 
and  maple  sugar  are  respectively  derived  from  the  stem  of 
the  sugar  cane  and  of  the  maple  tree.    The  sugar  maple  is 
tapped  for  its  sap  for  sugar-making  in  early  spring.    The  flow 
of  sap  is  most  abundant  during  moderately  warm  days  suc- 
ceeding freezing  nights.    A  single  tree  usually  yields  from 
30  to  50  or  more  quarts  of  sap,  from  which  3  or  4  pounds  of 
sugar  can  be  made.    One  tree  has,  however,  been  known  to 
yield   23  pounds  of    sugar  in  a  single  season.    Asparagus, 
cabbage,  and  a  few  other  vegetables  consist  of  aerial  shoots. 
Sago  is  made  from  the  starchy  pith  of  East  Indian  palms  and 
West  Indian  cycads.    Potatoes,  onions,  and  Jerusalem  arti- 
chokes are  well-known  examples  of  underground  stems  used 
as  food.   Many  familiar  animals  —  such  as  rabbits  (more  prop- 
erly called  hares),  deer,  and  moose  —  live  largely  by  brows- 
ing on  the  twigs  of  trees  and  shrubs.    In  pioneer  times  it  was 
sometimes  necessary  to  feed  to  horses  cottonwood  and  other 
twigs  in  winter  for  lack  of  hay.    Young  cornstalks  with  the 
leaves  (corn  fodder)  form  an  important  article  of  horse  and 
cattle  food,  and  the  preparation  of  fermented  cornstalks  known 
as  ensilage  is  widely  used.    The  stems  of  prickly-pear  cactus 
(Fig.  65)  deprived  of  their  thorns  (or  of  thorn  less  varieties 
of  this  cactus),  are  used  as  food  for  cattle  in  the  semi-desert 
regions  of  the  Southwest. 

75.  Reproduction  by  portions  of  the  stem.    The  number  of 
seed  plants  which  are  naturally  reproduced  by  means  of  por- 
tions of  the  stem  is  very  large,  and  there  are  many  others 
which  are  artificially  propagated  by  this  means.    Some  of  the 
principal  varieties  of  reproduction  by  pieces  of  stem  or  special 
shoots  for  the  purpose  are : 

(1)  By  aerial  bulblets. 

(2)  By  underground  bulbs,  rootstocks,  tubers,  and  so  on. 

(3)  By  offsets,  stolons,  and  runners. 

(4)  By  broken-off  branches  (Sect.  60)  or  cuttings  ("slips"). 


FIG.  66.  Steps  in  the  development  of  the  yellow  dogtooth  violet  (Erythro- 
nium  americanum)  from  the  seed  to  the  seventh  year 

The  diagram  for  the  most  part  explains  itself.  The  student  should  note  that  the 
seed  begins  to  germinate  late  in  the  first  year,  becoming  a  seedling  early  in  the 
second  year.  The  cotyledon  of  the  seedling  accomplishes  enough  food  making  by 
photosynthesis  to  enable  the  plant  to  form  a  small  bulb.  This  is  maintained  with- 
out much  increase  in  size  throughout  the  third  year.  During  the  fourth,  the  fifth, 
and  the  sixth  years  the  increasing  size  of  the  leaf  permits  the  production  of  larger 
and  larger  bulbs,  until  in  the  seventh  year  enough  plant  food  has  been  accumu- 
lated in  the  bulb  to  send  up  two  leaves  and  produce  a  flower  and  fruit.  The  third 
bulb  may  repeat  itself  indefinitely,  not  gaining  much  in  depth.  In  this  case  the 
interval  between  germination  and  flowering  would  be  more  than  six  years  (the 
time  indicated  in  the  diagram).  Each  well-developed  bulb  may  (in  this  species) 
form  runners,  rh,  which  bring  about  vegetative  reproduction,  the  small  bulb  at  the 
end  of  each  growing  into  a  new  plant.  Modified  after  Blodgett 


84 


PRACTICAL  BOTANY 


76.  Reproduction  by  bulblets  and  by  underground  stems. 
Many  plants  bear  small  aerial  bulbs  or  tubers  on  some  portion 
of  the  stem  and  are  commonly  reproduced  by  these.  Familiar 
examples  among  cultivated  plants  are  the  onion  and  the  tiger 
lily.  The  bulblets  known  as  "  onion-sets  "  are  for  sale  at  every 
seed  store,  and  in  some  parts  of  the  country  are  almost  exclu- 
sively planted  by  onion  growers,  while  in  other  sections  the 
seed  is  more  generally  planted.  The  black  bulblets  of  the  tiger 
lily  are  borne  in  considerable  numbers  along  the  stem,  in  the 


FIG.  67.  Roots,  rootstocks,  and  a  tuber  of  the  Jerusalem  artichoke 
(Helianthus  tuberosus) 

A,  base  of  a  plant  with  two  long  rootstocks,  about  one  twelfth  natural  size ;  B,  a 

full-grown  tuber,  beginning  to  sprout,  slightly  reduced ;  st,  aerial  stem ;  r,  roots ; 

rh,  rootstocks ;  I,  lateral  buds  of  tuber ;  t,  terminal  bud  of  tuber.    A,  modified 

from  report  of  Kansas  Agricultural  Experiment  Station 

leaf  axils,  and  may  be  found  on  the  ground,  rooting  in  the  late 
autumn  and  the  following  spring.  Some  of  our  wild  plants, 
including  certain,  ferns,  are  propagated  by  bulblets. 

Underground  stems  of  various  kinds  are  so  common  as  means 
of  reproduction  that  only  a  very  few  of  them  need  be  mentioned. 
Some  of  the  worst  weeds  are  those  which  have  running  root- 
stocks,  like  the  couch  grass  or  quack  grass  and  the  Canada  thistle, 
which  may  be  cut  up  by  the  hoe  and  produce  a  new  plant  from 
every  node ;  and  the  nut  grass  (Cyperus),  which  produces 
many  little  tubers.  Among  cultivated  plants  a  great  number 


REPRODUCTION  BY  STEMS  AND  LEAVES         85 


of  the  earliest  blooming  herbaceous  kinds,  such  as  squills, 
hyacinths,  tulips,  crocuses,  and  snowdrops,  are  grown  from 
bulbs  or  other  forms  of  underground  stem.  The  commonest 
of  all  instances  of  propagation  by  this  kind  of  stem  is  that  of 
the  potato,  which  is  never  grown  from  seed  except  for  the 
production  of  new  varieties.  As  every  farmer  and  market  gar- 
dener knows,  each  potato  will  produce  as  many  new  plants  as 

it  has  buds  ("eyes");  though 
it  is  better  not  to  cut  the 
potato  into  too  small  pieces 
for  propagation,  or  the  plants 
will  grow  slowly  at  first. 


FIG.  68.  Propagation  of  the  strawberry  plant  by  runners 
A,  the  parent  plant;  J5,  the  young  plant;  r,  runner;  6,  bract.   Half  natural  size 

77.  Reproduction  by  offsets  and  similar  branches.  An  offset 
is  a  lateral  branch  for  vegetative  reproduction,  usually  rather 
short,  as  seen  in  the  cardinal  flower  and  the  houseleek.  Some- 
times the  offset  ends  in  a  leafy  rosette ;  in  any  case  the  branch 
readily  takes  root  and  begins  life  as  a  new  individual. 

A  stolon  is  an  ordinary  branch  which  roots  at  or  near  the  tip 
and  so  forms  a  new  plant,  as  is  often  seen  in  the  black  raspberry. 
A  runner  is  a  very  slender  stolon,  leafless  except  near  the  tip, 
where  it  roots  and  grows  into  a  new  plant,  as  in  the  straw- 
berry (Fig.  68),  the  silverweed,  and  other  cinquefoils.1 

1  The  word  runner  is  also  used,  for  lack  of  a  better  term,  for  the  slender 
underground  stems  shown  in  Fig.  66. 


86 


PRACTICAL  BOTANY 


78.  Reproduction  by  detached  branches.  A  few  words  were 
said  in  Sect.  60  about  how  some  trees,  such  as  snap  willows, 
are  reproduced  by  broken-off  twigs,  rooting  like  cuttings. 

A  good  many  water  plants, 
such  as  the  common  bladder- 
wort,  produce  leafy  buds  or 
branch  tips  (Fig.  36 2)  which 
become  detached  from  the 
parent  plant.  In  late  autumn 
the  latter  usually  dies,  and 
in  the  spring  new  individuals 
arise  from  the  buds  which 
have  lain  dormant  all  winter 
at  the  bottoms  of  the  ponds  or 
slow  streams  where  they  grew. 
Numerous  woody  plants, 
such  as  willows,  grapevines, 
currant  bushes,  gooseberry 
bushes,  and  geraniums,  and 
some  herbaceous  plants  such 
as  the  hop  vine  and  the  Wan- 
dering Jew,  are  usually  grown 
from  cuttings.  Many  others, 
such  as  the  French  marigold 
and  the  garden  portulaca,  not 
usually  thus  grown,  may  be 
readily  propagated  by  cut- 
tings. In  the  case  of  woody 
plants  the  cutting  should  be 
taken  from  well-matured  twigs 
of  the  previous  season.  In 
order  to  avoid  too  much  loss 
of  water  and  consequent  wilt- 
ing, leafy  cuttings  are  often 

FIG.  69.  A  geranium  cutting,  show-      ,    '  i   «• 

ing  growth  of  many  young  roots  which     kept  covered  for  a  short  time, 
spring  from  a  node  near  the  cut  end      with  a  tumbler  Q?  feell  glass* 


BEPBODUCTION  BY  STEMS  AND  LEAVES        87 


Layering  is  a  modification  of  reproduction  by  cuttings,  and 
consists  in  bending  down  a  living  branch  and  covering  it  for 
part  of  its  length  with  earth,  so  as  to  form  a  sort  of  artificial 
stolon.  Some  trees  and  shrubs,  such  as  the  apple,  pear,  plum, 
and  quince,  are  much  easier  to  grow  by  layering  than  by  mak- 
ing cuttings,  and  they  root  more  readily  if  the  shoot  is  deeply 
notched  or  has  a  ring  of  bark  removed  on  the  buried  portion. 


ABC 

FIG.  70.  Propagation  by  budding 

A,  a  bud  cut  from  a  tree  of  the  desired  variety,  with  a  piece  of  the  underlying 

bark;  B,  the  bud  inserted  in  a  T-shaped  slit  in  the  bark  of  the  stock;  C,  the 

same,  with  the  bark  bound  in  place  by  strips  of  raffia  (a  fibrous  material  obtained 

from  the  leaves  of  the  raffia  palm) .  Modified  after  Percival 

79.  Budding  and  grafting.  The  process  of  budding  consists 
of  detaching  an  uninjured  bud  from  the  stem  of  one  plant 
and  inserting  it  under  the  bark  of  the  stem  of  another  plant 
(Fig.  70).  Peaches  and  cherries  are  familiar  examples  of  trees 
commonly  propagated  by  budding.  The  operation  should  be 
performed  at  a  season  when  the  cambium  layer  is  active,  so 
that  the  transplanted  bud  will  at  once  unite  with  the  wood 
of  the  stem  into  which  it  is  set.  In  the  case  of  peaches  the 
young  seedling  trees  grown  from  seeds  planted  the  same 
spring  are  budded  in  June  or  September.  Those  budded  late 
do  not  grow  much  until  the  next  season,  but  then  make  rapid 


88 


PRACTICAL  BOTANY 


progress.  As  the  top  of  the  seedling  is  cut  off  not  far  above 
the  bud,  all  further  growth  of  the  shoot  partakes  of  the 
quality  of  the  bud ;  and  the  fruit  borne  by  the  tree,  when  it 
is  large  enough  to  bear,  will  be  of  the  kind  characteristic  of 
the  tree  from  which  the  bud  was  taken. 

Grafting  is  removing  a  piece  of  stem 
with  its  buds  from  one  plant  and  inserting 
it  into  a  portion  of  stem  of  another  living 
plant  so  that  the  cambium  layer  of  each 
will  be  in  contact  with  that  of  the  other 
(Fig.  71).  The  plant  into  which  the  stem 
is  inserted  is  called  the  stock,  and  the  por- 
tion of  shoot  which  is  set  into  the  stock  is 
called  the  scion  or  graft.  There  are  many 
kinds  of  woody  plants  which  may  readily 
be  grafted,  but  the  process  is  of  practical 
importance  mainly  for  the  grower  of  apples 
and  pears.  Various  plans  are  adopted  in 
different  fruit-growing  regions.  One  of  the 
commonest  methods  for  the  propagation  of 
apples  is  root  grafting.  Seedling  trees  a 
year  old  are  dug  in  the  autumn  and  the 
roots  grafted  with  one-year-old  scions  of 
desired  varieties  of  apples,  each  cut  to  the 
length  of  about  six  inches.  The  grafted 
roots,  wound  about  the  joined  surfaces  with 
waxed  cord,  are  packed  in  sand  in  a  cool 
and  not  too  dry  cellar  and  left  until  spring. 
By  that  time  the  cambium  layers  of  root 
and  scion  have  united  .and  the  roots  are 
ready  to  plant.  Tongue  grafting  is  practiced  either  with  young 
seedlings  or  with  twigs  of  larger  trees  (Fig.  71)  in  the  spring. 
Top  grafting  consists  in  cutting  off  limbs  one  or  two  inches  in 
diameter,  splitting  the  portion  remaining  attached  to  the  tree 
for  a  short  distance,  and  inserting  at  each  part  of  the  split, 
where  it  crosses  the  cut  surface,  a  small  scion,  and  then 


FIG.  71.  Grafting 

At  the  left  scion  and 
stock  are  shown  ready 
to  be  united;  at  the 
right  they  are  joined 
and  ready  to  cover 
with  grafting  wax. 
After  Percival 


REPRODUCTION  BY  STEMS  AND  LEAVES    89 

covering  all  exposed  parts  well  with  grafting  wax.  Root  graft- 
ing has  the  advantage  that  it  results  in  a  tree  with  trunk  and 
branches  wholly  of  the  desired  variety  of  apple.  Tongue 
grafting  of  small  branches  does  not  interrupt  the  growth  of 
the  tree  and  is  done  with  very  little  trouble.  Top  grafting  is 
mainly  resorted  to  in  order  to  renew  old  trees  that  are  not 
bearing  the  desired  variety  of  apple. 

The  main  object  of  budding  and  grafting  is  to  propagate 
the  varieties  of  fruit  which  the  horticulturist  desires.  This 
cannot  be  done  merely  by  growing  seedling  trees,  since  every 
seedling  of  hundreds  grown  from  any  valuable  kind  of  apple 
or  pear  may  differ  from  all  the  others  of  the  same  lot  and  not 
one  of  them  be  worth  cultivating. 

Grafting  often  succeeds  on  plants  of  different  species,1  as 
the  peach  on  the  plum,  the  apple  on  the  pear,  and  the  pear 
on  the  quince.  Sometimes  it  succeeds  between  different 
genera 1  of  the  same  family,1  as  the  tomato  on  the  potato  and 
the  Spanish  chestnut  on  the  oak. 

Many  technical  details  must  be  attended  to  in  order  to  bud 
or  graft  successfully,  and  these  are  best  learned  from  a  practical 
horticulturist. 

80.  Reproduction  by  leaves.  Not  very  many  plants  can  re- 
produce themselves  by  means  of  their  leaves.  The  best-known 
examples  are  begonias,  which  are  largely  propagated  by  cut- 
ting off  leaves,  slitting  them,  and  then  laying  them  on  moist 
sand  under  a  bell  glass  until  buds  and  roots  are  produced 
at  one  or  more  points  of  the  cut  surface.  A  not  uncommon 
greenhouse  plant  of  the  Live-forever  family,  the  Bryophyllum, 
is  still  more  easily  propagated,  as  the  leaflets  readily  produce 
buds  and  roots  at  the  notches  along  their  margins  when  placed 
on  moist  earth. 

1  For  the  definition  of  the  terms  "species,"  "genus,"  and  "family,"  see 
Chapter  X- 


CHAPTER  VI 


BUDS  AND  BRANCHES 

81.  Naked  buds  and  scaly  buds.  When  people  who  are  not 
botanists  speak  of  buds,  as,  for  example,  in  referring  to  the 
signs  of  leaf- 
ing or  flower- 
ing of  fruit 
trees  in  the 
spring,  they 
always  mean 


Fi'j.  72.  Twigs  of  black 

walnut  with   buds   in 

winter  condition 

Two  thirds  natural  size 


the  scaly  winter  buds  or  resting  buds,  such 
as  are  familiar  on  most  of  our  hard-wood 
trees  and  shrubs  (Figs.  72-86).  This  is, 
however,  a  narrow  view  of  the  meaning 
of  the  term.  Herbs  like  our  common  gar- 
den annuals,  such  as  the  bean,  the  pea,  the 
cucumber,  and  the  morning-glory,  are 
as  well  provided  with  buds  in  proportion 
to  their  size  as  are  ordinary  trees.  In  the 
tropical  rain  forest,  where  the  tempera- 
ture is  always  high  and  there  are  violent  rains  almost  daily, 
there  are  few  scaly  buds.  Most  of  the  trees  in  such  regions  have 
naked  buds  like  those  of  the  common  greenhouse  hydrangea 
(Hydrangea  Hortensia)  or  the  geraniums  (^Pelargonium). 

Generally  speaking,  scaly  buds  occur  in  woody  plants  which 
grow  in  cold  or  temperate  climates,  where  such  buds  are  well 
suited  to  resist  the  sudden  winter  changes  from  heat  to  cold, 
and  the  reverse.  Some  of  our  common  trees  and  shrubs  have 
buds  which  are  only  slightly  protected  by  scales,  but  these 
buds  are  usually  small,  and  often  more  or  less  hidden  under 
the  bark,  as  in  the  syringa  (Philadelphus)  and  the  Ailanthus. 

90 


BUDS  AND  SEARCHES 


91 


82.  Nature  of  the  bud  and  its  coverings.  A  bud  is  an  unde- 
veloped shoot;  or,  in  other  words,  a  bud  is  a  group  of  undevel- 
oped parts  which,  under  favorable  circumstances,  will  grow 
into  some  kind  of  stem  and  leaves.  If  it  is  a  leaf  bud,  like  the 
majority  of  the  buds  on  most  forest  trees  familiar  to  us,  it  will 
grow  into  a  leafy  branch  or  con- 
tinue the  growth  of  the  main  stem 
at  its  tip.  If  it  is  a  flower  bud,  it 
will  grow  into  that  kind  of  spe- 
cialized branch  which  we  call  a 
flower.  If  it  is  a  mixed  bud,  it  will 
grow  into  one  or  more  flowers  and 
will  also  develop  some  ordinary 
leaves. 

The  scales  which  cover  buds 
are  often  dwarfed  and  otherwise 
modified  leaves  or  leafstalks,  as 
is  well  shown  in  some  buckeyes 
in  which  the  opening  buds  present 
a  series  of  gradations  between 
mere  scales  and  foliage  leaves 
(Fig.  73).  In  other  cases,  as  in 
oaks,  beeches,  lindens,  and  mag- 
nolias, the  scales  represent  the 
appendages  (stipules')  found  at 
the  bases  of  many  leaves.1  Fre- 
quently bud  scales  are  covered 
with  a  dense  layer  of  hairs  or 
down,  and  sometimes,  as  in  the 
balm-of-Gilead  poplar,  they  are 

cemented  together  by  a  resinous  varnish.  These  coatings  on 
the  scales  of  materials  which  do  not  readily  conduct  heat  in- 
crease their  value  as  a  protection  against  sudden  changes  in  the 
weather  during  the  colder  months. 

1  See  Kerner-Oliver,  Natural   History  of  Plants,  Vol.  I,  pp.  351-353. 
Henry  Holt  and  Company,  New  York. 


FIG.  73.  Dissected  bud  of  sweet 

buckey  e,'showing  transitions  from 

bud  scales  to  leaves 


92 


PRACTICAL  BOTANY 


\--ax 


83.  Position  of  buds.  Buds  are  either  terminal,  growing  from 
the  tip  of  the  stem ;  or  lateral,  growing  from  its  side  (Fig.  74, 
lat).  The  plumule  (Fig.  126)  is  the  first  terminal  bud  of  the 
young  seedling.  Commonly  the  terminal 
bud  is  stronger  than  any  of  the  lateral 
ones,  and  makes  more  rapid  growth  than 
they  do. 

Lateral  buds  are  usually  axillary ;  that 
is,  they  arise  from  the  axil,  or  angle, 
formed  by  the  leaf  with  the  stem,  as 
shown  in  Fig.  74,  ax.  Many  plants  also 
produce  accessory  buds;  that  is,  buds  a 
little  outside  of  the  leaf  axil,  which  may 
either  stand  above  the  axillary  bud,  as  in 
the  butternut,  or  on  either  side  of  it,  as 
in  the  box  elder  (Fig.  75). 

Adventitious  buds  are  those  which  spring, 
without  any  definite  order,  from  roots, 
stems,  or  leaves.  These  are  often  of  great 
value  in  propagating  plants  by  means  of 
cuttings  or  layers. 

84.  Form  of  trees  dependent  on  growth 
of  buds.  If  the  uppermost  bud  of  the  main 
stem  of  a  tree  continues  year  after  year 
to  be  stronger  than  any  other  bud,  the 
general  form  of  the  tree  becomes  roughly 
conical,  as  is  well  shown  in  the  pine  tree 
(Fig.  246),  and  in  firs,  spruces,  and  the 
European  cypress.  If,  on  the  other  hand, 
some  of  the  branches  grow  in  length  as 
fast  as  the  main  trunk,  the  tree  will  be- 
come round-topped  and  spreading,  like  an  apple  tree,  an  elm,  or 
most  of  our  hard-wood  trees,  when  they  grow  in  open  ground. 
Not  uncommonly  the  terminal  bud  of  most  branches  is  a 
flower  bud,  as  in  the  magnolias,  or  no  terminal  bud  is  devel- 
oped, as  in  the  lilac.  In  these  cases  the  main  branches  cannot 


FIG.  74.  Twig  of  hick- 
ory in  winter  condition 

sc,  scar  of  last  year's 
leaf;  lat,  a  lateral  bud; 
I,  a  last  year's  leafstalk ; 
ax,  a  lateral  bud  in  the 
axil  of  the  leafstalk ;  t, 
terminal  bud.  Reduced 


BUDS  AND  BRANCHES 


93 


run  out  from  the  trunk  for  long  distances,  remaining  much 
larger  than  any  of  the  branchlets,  as  they  do  in  the  spruces 
and  in  many  pines  (Fig.  329).  Why  can  they  not?  Such 
trees  are  round-topped,  with  many  forking  branches. 

85.  Competition  among  buds  and  branches.  Of  all  the  buds 
yearly  produced  by  a  medium-sized  tree  only  a  small  propor- 
tion can  survive  even  for  a  year  or  two,  and  a  much  smaller 
proportion  still  can  grow  into 
branches.  The  killing-off  proc- 
ess is  mainly  one  of  light- 
starvation.  Looking  up  into 
the  crown  of  a  tree  along  a 
line  nearly  parallel  to  its 
trunk,  one  is  able  readily  to 
see  that  the  tree  top  is  not 
a  rather  dense  mass  of  leaf- 
covered  twigs,  as  it  appears 
to  be  when  looked  at  from 
without.  It  is  more  nearly  a 
hollow  cone  or  (in  the  case 
of  very  round-topped  trees) 
a  hemisphere,  like  an  open 
umbrella,  the  main  branches 
answering  to  the  ribs  of  the 
umbrella.  The  interior  por- 
tion of  the  tree  top  is  too  much  shaded  for  rapid  growth  of 
buds  or  young  twigs,  and  parts  of  it  are  dark  enough  to  kill 
them  outright,  since  their  growth  depends  upon  the  plant 
food  which  they  can  make  by  photosynthesis. 

Some  simple  counts  and  calculations  may  serve  to  make 
clearer  the  fact  of  competition  and  consequent  death  of  the 
interior  members  of  the  tree  top.  On  a  well-grown  box-elder 
tree,  perhaps  twenty-five  years  old,  the  condition  of  the  lateral 
twigs  springing  from  six-year-old  portions  of  the  smaller 
branches  was  carefully  noted  in  March.  On  the  branches 
most  fully  exposed  to  the  sun,  on  the  south  side  of  the  tree, 


li 


FIG.  75.  Accessory  buds  of  box  elder 
(Acer  Negundo).   Magnified 

A,  front  view  of  group;  B,  two  groups 
seen  in  profile 


94 


PRACTICAL  BOTANY 


the  number  of  lateral  twigs  on  the  six -year-old  portions  of  the 
branches  ranged  from  0  to  9  and  averaged  3.2.1  On  the  north 
side  of  the  tree,  and  somewhat  inside  its  circumference,  only 


FIG.  76.  Development  of  leaf  bud  of  pear 

A,  a  leaf  bud  of  pear  in  autumn;  £,  a  leafy  shoot  derived  from  A,  as  seen  in 

the  middle  of  the  following  summer,  with  flower  bud  at  tip ;   C,  the  fruit  spur 

(5)  in  autumn,  after  the  falling  of  the  leaves.    After  Percival 


FIG.  77.  Fruit  bud  of  pear  (same  as  C  of  Fig.  76),  showing  its  development 

A,  opening  in  spring ;  B,  later,  developing  flowers  and  leaves ;  C,  later  still ;  only 

one  flower  has  produced  a  fruit,  the  rest  having  fallen  off.   Below  it,  is  a  lateral 

bud  which  will  continue  the  spur  next  year.   After  Percival 

1  Average  of  ten  counts. 


BUDS  AND  BKANCHES  95 

one  branch  out  of  ten  had  any  live  twigs.  The  sunlighted 
branches,  then,  had  32  times  as  many  twigs  on  the  portions 
counted  as  the  shaded  ones  did.  A  similar  study  of  a  large 
thorn  bush  (^Cratcegus)  gave  for  the  ten  sunlighted  branches 
74  live  twigs  and  for  the  shaded  ones  only  2,  or  37  times 
as  many  for  the  sunny  side.1  A  study  of  the  relative  amount 
of  growth  of  the  tips  of  branches  during  the  year  preceding 
the  observations  showed  that  those  on  the  sunny  side  of  the 
thorn  grew  21  times  as  fast  as  those  on  the  shady  side.2 

86.  Definite  and  indefinite  annual  growth.  In  such  trees  as 
the  hickories,  walnuts,  butternuts,  elms,  poplars,  and  so  on 
(Figs.  72,  74,  82),  the  branches  usually  produce  vigorous, 
well-matured  buds  at  their  tips ;  that  is,  they  form  definite 
shoots,  and  each  terminal  bud  develops  promptly  in  the  spring. 
But  some  trees,  like  the  honey  locust,  and  such  shrubs  as 
sumachs,  roses,  raspberries,  and  blackberries,  form  indefinite 
shoots,  which  grow  until  their  tips  are  killed  by  the  frost. 
Trees  of  this  sort  necessarily  have  a  top  much  broken  up  into 
minor  branches.    Why? 

87.  Fruit  spurs.  A  fruit  spur  is  a  short  fruit-bearing  twig 
borne  on  the  side  of  a  branch  (Figs.  76  and  77).    Apple,  pear, 
plum,  and  cherry  trees  afford  capital  examples  of  the  production 
of  fruit  spurs.    At  the  tip  of  the  spur  a  flower  bud  (or  a  mixed 
bud)  is  borne,  and  this  usually  develops  into  a  cluster  of  flowers, 
one  or  more  of  which  may  mature  into  fruit.    In  the  apple  and 
pear  (Fig.  77),  though  the  flower  bud  contains  a  good  many 
blossoms,  only  one  fruit  is  generally  produced  from  each  bud. 
In  cherries  a  single  bud  produces  a  cluster  of  fruits.   Why  ? 

If  the  terminal  bud  of  the  spur  contained  leaves  as  well  as 
flowers,  a  leaf  bud  is  likely  to  grow  in  the  axil  of  one  of  the 
leaves  and  thus  provide  for  the  growth  of  the  spur  during 
another  year.  This  process  may  go  on  for  a  good  many  years. 

1  Comparing  three-year-old  portions  of  branches. 

2  The  illumination  in  the  shade   (measured  by  "solio"   photographic 
printing  paper)  was,  for  the  box  elder,  about  one  twentieth  and  for  the  thorn 
about  one  eightieth  that  of  the  sunny  side  at  noon  in  early  July. 


96 


PRACTICAL  BOTANY 


Evidently  when  the  spur  produces  a  terminal  bud  contain- 
ing flowers  it  cannot  grow  straight  ahead  but  must  turn  aside 


FIG.  79.  Cross  section  of  a  poplar  bud 

sc,  bud  scales ;  I,  leaves ;  st,  stipules.  Magnified 
15  diameters.   After  Strasburger 


FIG.  78.  A  lengthwise 

section  of  bud  of  thorn 

tree  (Cratcegus) 

br,  brown  outer  bud 
scales ;  o,  pale  bud  scale ; 
t,  innermost  rudimentary 
leaves ;  gr,  growing  point 
at  apex  of  twig,  consisting 
of  cells  in  a  condition  to 
sub-divide  and  multiply 
rapidly  at  the  beginning 
of  the  growing  season. 
Somewhat  magnified 

slightly.  Since  a  large  part 
of  the  plant  food  carried  into 
the  spur  is  used  in  produc- 
ing the  flowers  and  fruit,  it 
is  clear  that  a  fruit  spur 
cannot  grow  as  rapidly  as 
an  ordinary  twig.  A  little 
study  of  an  old  fruit  spur 
will  show  that  of  the  .scars 
left  by  the  flower  buds 


FIG.  80.  American  elm,  March  11 

The  large  buds  are  flower  buds,  the  smaller, 
more  numerous  ones,  leaf  buds.    Reduced 


FIG.  81.  American  elm,  April  3 
flower  buds  seen  in  Fig.  80  are  fully  opened.  Reduced 

97 


98 


PRACTICAL  BOTANY 


some  are  much  larger  than  others.  The  large  scars  mark 
seasons  when  the  fruit  matured,  and  much  smaller  ones  show 
that  it  dropped  before  it  was  full  grown. 
Do  fruits  generally  mature  on  any  given 
fruit  spur  two  years  in  succession  ? l 

88.  Structure  of  leaf  buds.  Scaly  win- 
ter leaf  buds  consist,  as  shown  in  Figs.  78 


FIG.  82.  Twig  of  cotton- 
wood  with  buds  in  winter 
condition 

b.sc,  bud-scale  scars.  Two 
thirds  natural  size 


J 


FIG.  83.  Cottonwood  twigs,  April  15 

The  flower  buds  (developing  into  catkins) 

are  fully  open,  but  the  leaf  buds  are  still 

closed.  Reduced 


and  79,  of  (a)  one  or  more  outer  layers  of  scales ;  (£>)  rudimen- 
tary leaves ;  (e)  a  central  axis,  at  the  tip  of  which  is  the  growing 
point  (Fig.  36),  a  region  of  cells  capable  of  rapid  sub-division, 
by  means  of  which  the  elongation  of  the  shoot  is  produced. 

1  See  Bailey,  Lessons  with  Plants,  Part  I.   The  Macmillan  Company, 
New  York. 


BUDS  AND  BRANCHES  99 

The  rudimentary  leaves  are  stowed  in  the  bud  in  a  Avonder- 
fully  compact  manner.  There  are  several  plans  of  arrange- 
ment, all  of  which  have  received  technical  names.  The  mode 


FIG.  84.  Cottonwood  fruits,  April  28  , 
Reduced 

of  arrangement  is  best  shown  in  a  cross  section  of  the  bud 
like  that  represented  in  Fig.  79. 

In  mixed  buds,  as  a  rule,  the  flowers  are  inclosed  by  the 
leaves  and  usually  develop  earlier  than  the  leaves  (Fig.  83). 

89.  Opening  of  buds.  Winter  buds  are  not  absolutely  inac- 
tive during  the  colder  months.  Often  a  gradual  increase  in 
the  size  of  the  bud  can  be  noted  for  many  weeks  before  it 


100 


PEACTICAL  BOTANY 


gives  any  other  external  sign  of  getting  ready  to  open.    This 
swelling  is  caused  by  the  growth  and  development  of  the  leaves 


or  other  contents  of  the  bud.  When  the 
begins  to  open,  the  scales  spread  apart 
contents  to  emerge;  sometimes  they 
off.  It  is  this  time  when  the  flowers 
to   open  that   is   a  particularly 
the  fruit  grower.   Peaches,  for 
to  blossom  before  the  last 
season  are  over,  and  the 


FIG.  85.  Rapidly  grown  twigs  of  horse- 
chestnut  in  winter  condition 

b.sc,  bud-scale  scars ;  ii,  i%,  is,  internodes ; 
I,  lateral  buds ;  t,  terminal  buds ;  sc,  leaf 
scars.  The  portion  i^-i^  and  the  large 
terminal  bud  grew  during  the  preceding 
spring  and  summer.  The  opposite  lateral 
twigs  are  of  the  same  age  as  the  portion 
ii-is.  One  third  natural  size 

the  coldest  month  is  often 

March  or  April,  after  the  young  olive  leaves  are  fairly  well 
grown  and  are  not  easily  injured  by  cold. 


bud  actually 
and  allow  the 
promptly  fall 
are  beginning 
anxious   one   for 
example,  often  begin 
freezing  nights  of  the 
entire  crop  may  often  be 
cut  off  by  a  single  very  cold 
night.  For  this  reason  peach- 
growing  in  the  North  is  safest 
in  regions,  like  the  east  shore 
of  Lake  Michigan,  where  the 
spring  is  usually  rather  late  in 
coming.    A  curious  instance 
of  the  importance  of  the  sea- 
son at  which   frosts    occur 
is  found  in  European  olive 
culture.    In  the  Crimea,  on 
the  north  shore  of  the  Black 
Sea,  the  temperature  during 
most  years  sinks  a  good  deal 
lower  than  it  does  in  southern 
France.    Yet  in  Languedoc 
the  olive  culture  fails,  while 
in  the    southern  Crimea  it 
succeeds,     because     in    the 
former  region  severe  frosts 
occur  in  January,  just  when 
the  olive  buds  are  opening, 
while    in  the   latter   region 


BUDS  AND  BRANCHES 


90.  The  record  borne  by  the  twig.  In  most  cases  the  twig 
bears  upon  its  surface  and  in  its  rings  of  wood  a  fairly  com- 
plete record  of  the  most  important  events  of  its  Me.    Some  of 
the  principal  markings  on  the  surface  of  a 

twig  which  enable  us  to  make  out  its  history 
are :  (a)  bud-scale  scars  (from  leaf  buds) ; 
(5)  fruit  scars ;  (c>)  leaf  scars.  Other  mark- 
ings are  found  which  tell  less  of  the  life 
history  of  the  twig  than  those  just  enumer- 
ated, but  which  should  also  be  considered, 
namely,  (cT)  lenticels. 

The  bud-scale  scars,  as  the  name  implies, 
are  the  markings  (Figs.  82  and  85,  b.sc) 
left  by  the  falling  of  the  scales  when  the 
bud  opened.  Plants  like  geraniums,  with 
naked  buds,  do  not  show  such  scars.  As  the 
twig  or  branch  in  most  cases  is  prolonged 
by  the  growth,  spring  after  spring,  of  its 
terminal  bud,  each  ring  of  scars  marks  the 
beginning  of  a  new  season's  growth.  In 
many  trees  it  is  easy  to  determine  the  age 
of  twigs  or  branches  by  counting  the  number 
of  such  rings  (Fig.  86).  The  distance  be- 
tween the  rings  of  scars  depends  upon  the 
rapidity  of  growth  of  the  shoot  in  length, 
varying  all  the  way  from  a  fraction  of  an 
inch  to  ten  or  more  feet  per  year. 

If  a  twig  were  cut  across  smoothly,  just 
above  and  just  below  a  ring  of  bud-scale 
scars,  would  the  number  of  rings  of  wood 
in  the  two  sections  be  the  same  ?  Why,  or 
why  not  ? 

91.  The  record;  fruit  scars.  Fruit  scars  of  the  same  species 
are  often  quite  unequal  in  size,  the  smaller  ones  marking  the 
positions  of  unsuccessful  fruits,  and  the  larger  ones  of  fruits 
which  grew  to  maturity.    Sometimes  in  mixed  buds  the  young 


FIG.  86.    A  slowly 
grown  twig  of  horse- 
chestnut  in  winter 
condition 

d,  dormant  buds ;  fs, 
flower-cluster  scar. 
The  internodes  are 
numbered  in  succes- 
sion (beginning  at 
the  bottom)  with  the 
respective  years  dur- 
ing which  they  were 
formed.  One  third 
natural  size 


102 


^PRACTICAL  BOTANY 


FIG.  87.  Leaf  scar  of  horse- 
chestnut 

fv,  scars  marking  position  of  fibro- 

vascular  bundles ;  len,  lenticels. 

Twice  natural  size 


flowers  may  be  destroyed  by  frost  as  the  bud  opens,  and  in 

that  case  no  fruit  scar  will  be  left  at  the  end  of  the  season, 

the  bud  developing  much  like  an 
ordinary  leaf  bud. 

The  only  way  in  which  one  can 
become  thoroughly  familiar  with  the 
course  of  development  of  shoots, 
flowers,  and  fruits  from  buds  is  to 
mark  some  buds  like  that  shown  at 
A  in  Fig.  76.  This  may  be  done  by 
tying  a  bit  of  twine  loosely  above 
each  bud ;  its  history  is  then  to  be  fol- 
lowed for  at  least  a  year  and  recorded 
by  means  of  frequent  drawings. 

92.  The  record;  leaf  scars.  A  leaf 
scar  is  the  place  which  was  occupied 

by  the  base  of  the  leafstalk  while  it  remained  attached  to 

the  shoot.    Some  of  the  things  which  can  be  learned  from  the 

study  of  leaf  scars  are  the  number, 

position,  and  arrangement  of  leaves 

on  the  shoot  for  several  years  back, 

the  relative  sizes  of  the  leaves,  and 

the  mode  of  bud-bearing  of  the  spe- 
cies   studied,  —  i.e.    whether    there 

were   accessory  buds,   or  the  buds 

were  all  axillary  (Figs.  75  and  85). 

On  careful  examination  of  any  large 

leaf  scar,  as  that  of  ailanthus,  horse- 
chestnut  (Fig.  87),  coffee  bean,  it  is 

seen  to  be  dotted  with  a  considerable 

number  of  minute  projections,  fv. 

These  mark  the  course  of  the  fibro- 

vascular  bundles  from  the  leaf  into 

the  stem.    In  leaves  of  dicotyledons 

there  are  usually  about  as  many  such  dots  on  the  scar  as  there 

were  principal  veins  in  the  leaf.    Why  ? 


B 


FIG  .  88.  Lenticels,  wild  black 
cherry 

A,  soon  after  the  destruction  of 
the  stomata,  to  which  the  len- 
ticels succeed;  B,  at  end  of 
first  season's  growth.  One  and 
one-half  times  natural  size 


BUDS  AND  BRANCHES  103 

93.  Lenticels.  On  the  general  surface  of  the  bark  of  many 
kinds  of  twigs  and  young  branches  —  for  example,  of  birch, 
cherry,  elder,  and  sumach  —  there  are  found  many  dots,  or 
markings  with  a  rough  surface,  known  as  lenticels.  These  are 
nearly  circular  on  the  younger  twigs,  but  on  branches  of 
moderate  size  they  become  lengthened  at  right  angles  to  the 
length  of  the  branch.  In  many  kinds  of  birch  and  most 


FIG.  89.  Lenticels,  wild  black  cherry 
From  a  tree  fifteen  or  twenty  years  old.   One  and  one-half  times  natural  size 

cherries  the  lenticels  finally  become  narrowly  oblong  or  lens- 
shaped  (Fig.  89).  This  is  due  to  the  fact  that  as  the  branch 
increases  in  diameter  the  lenticel  is  drawn  out  by  the  trans- 
verse expansion  of  the  bark. 

Lenticels  originate  as  stomata  (Sect.  14)  in  the  epidermis 
of  the  young  shoot.  On  growing  older  the  interior  of  the 
lenticel  becomes  filled  with  a  spongy  mass  of  thin-walled  cells. 
Air  is  admitted  into  the  interior  of  the  stem  and  gases  can 
pass  out  through  the  lenticels  far  more  freely  than  through 
other  parts  of  the  bark. 


CHAPTER  VII 


FLOWERS 

94.  What  is  a  flower  ?  A  little  has  been  said  in  Chapter  II 
about  the  structure  and  work  of  the  flower,  but  it  will  be 
necessary  in  the  present  chapter  to  take  up  these  matters 

somewhat  more 

Corolla  •  /\  ^  m  detail.   First 

may  come  the 
question  as  to 
what  a  flower 
really  is ;  that  is 
to  say,  to  what 
other  organs  of 
a  plant  the  parts 
of  a  flower  cor- 
respond. Put  in 
more  technical 
language,  this 
question  would 
be,  What  is  the 
morphology  of 
the  flower  ? 

A  flower  is  a  specialized  and  highly  modified  branch  or  shoot 
for  reproduction  of  the  plant.  If  this  is  true,  then  the  sepals 
or  divisions  of  the  calyx,  petals  or  divisions  of  the  corolla, 
stamens,  and  pistils  (Fig.  90)  must  represent  leaves.  It 
would  take  too  much  space  to  present  here  the  evidence  of 
the  branch-like  nature  of  the  flower.  Much  of  this  evidence 
rests  upon  the  study  of  the  lower  plants,  and  especially  on 
the  investigation  of  the  steps  by  which  the  higher  kinds  of 
plants  have  in  the  course  of  ages  been  developed  from  these. 

104 


^Stamen 
^Pistil 


FIG.  90.  The  floral  organs  of  alpine  azalea  (Loiseleuria) 

A  good  example  of  a  flower  in  which  the  floral  organs  do^jot 
all  spring  separately  from  a  knoh-like  receptacle.  Here  the 
calyx  is  very  slightly  and  the  corolla  decidedly  bell-shaped. 
The  stamens  are  distinct  from  each  other,  but  the  pistil  is 
single  and  represents  several  united  carpels.  A,  an  exterior 
view ;  B,  a  lengthwise  section  of  the  flower.  After  H.  Miiller 


FLOWERS 


105 


95.  The  arrangement  of  the  organs  of  the  flower.  Many  of 
the  most  familiar  flowers  have  the  four  sets  of  organs  shown 
in  Figs.  90  and  92.  Sometimes  there  are  intermediate  forms, 


B  C       D     E     F 

FIG.  91.  Transitions  between  petals  and  stamens  in  the  yellow  pond  lily 

A,  external  view  of  flower ;  J5,  a  sepal ;  C,  a  petal ;  D,  E,  transitional  forms ; 

F,  a  stamen 

transitional  between  the  parts  of  one  set  and  those  of  another, 

—  a  fact  easily  understood  if  all  the  floral  organs  represent 
leaves.    The  organs  are  generally  arranged  in  cycles  or  whorls, 

—  that  is,  in  circular  fashion  around  the  axis,  which  is  known 
as  the  receptacle.1   Often  (but  not  always)  the  parts  of  each 


FIG.  92.  Flower  of  stonecrop 

A  typical  example  of  the  kind  of  flower  in  which  the  members  of  all  four  sets  of 
floral  organs  (sepals,  petals,  stamens,  and  carpels)  spring  separately  from  a  knob- 
like  receptacle.  A,  entire  flower ;  />,  vertical  section.  Bothmagnified.  After Decaisne 

set  stand  opposite  the  spaces  between  the  parts  of  the  adjoin- 
ing sets;  e.g.  the  petals  opposite  the  spaces  between  sepals, 
stamens  opposite  the  spaces  between  petals,  and  so  on. 

1  In  the  lowest  seed  plants,  the  gymnosperms  (pines,  spruces,  cedars,  and 
so  on),  the  parts  of  the  flower  are  arranged  in  a  spiral  fashion.  So,  too,  are 
some  of  the  floral  organs  in  the  arrowhead  (Sagittaria),  the  pond  lily,  and 
the  buttercup. 


106 


PRACTICAL  BOTANY 


FIG.  93.   Apetalous  flower  of  buckwheat  (Fagopyrum 
esculentum) 

A,  flower ;  B,  section  of  flower.  Both  somewhat  magnified. 
After  Marchand 


Frequently  the  arrangement  of  the  floral  organs  differs  from 

that  just  described  by  reason  of  the  absence  of  one  or  more 

sets  of  organs  or 
from  the  multi- 
plication of  the 
whorls.  In  the 
buckwheat,  for 
example  (Fig. 
93),  only  one 
whorl  surrounds 
the  stamens  and 
pistil.  In  such 
cases  it  is  usual 

to  assume  that  the  missing  flower  leaves  are  the  petals,  and 

the  flower  is  said  to  be  apetalous  (without  petals).    Sometimes 

neither  sepals  nor  petals  are  found  (Fig.  94).    On  the  other 

hand,  many  flowers  have 

both  calyx  and  corolla, 

with  the  number  of  petals 

equal    to    that    of    the 

sepals,  but  with  indefi- 
nitely numerous  stamens, 

as  in  buttercups. 

96.  Unisexual  flowers. 

Among    many    families 

of  plants  the  flowers  do 

not  contain  both  stamens 

and  pistils.   One  kind  of 

flower  has  stamens  only, 

and  is  called  a  staminate 

flower,  while  the   other  A 

kind  has  pistils  only,  and 

is  called  &  pistillate  flower 

(Figs.  94  and  96).  Such 

flowers   are   said  to  be 

unisexual  or  diclinous. 


D 


FIG.  94.   Dioecious  flowers  of  white  willow 
(Salix  alba) 

A,  staminate  catkin,  natural  size ;  B,  pistillate 

catkin,  natural  size;    C,  a  staminate  flower, 

magnified ;   D,  a  pistillate  flower,  magnified. 

After  Cosson  and  De  Saint-Pierre 


FLOWEBS 


107 


Sometimes,  as  in  corn  and  cucumbers,  one  plant  bears  both 
staminate  and  pistillate  flowers.  Such  plants  are  said  to  be 
monoecious  (meaning  "of  one  household").  Many  plants,  such 


FIG.  95.  Catkins  of  willow 
Pistillate  catkins  at  the  left ;  staminate  at  the  right.   Slightly  reduced 

as  willows  and  poplars,  bear  the  staminate  and  the  pistillate 
flowers  on  different  individuals.  Such  plants  are  said  to  be 
dioecious  (meaning  "of  two  households"). 


108 


PRACTICAL  BOTANY, 


It  is  often  a  matter  of  much  practical  importance  to  recognize 
the  partially  or  completely  dioecious  character  of  cultivated 
plants,  or,  at  any  rate,  the  fact  that  many  or  all  of  the  individ- 
uals of  a  species  or  variety  produce  no  good  pollen.  This  is  well 
known  to  be  true  of  strawberries,  and  so  staminate  varieties 
must  be  planted  among  those  which  produce  little  or  no  pollen. 
97.  Symmetry  of  the  flower.  The  calyx  and  corolla  of  most 
flowers  of  the  higher  seed  plants  show  some  kind  of  symmetry 

or  orderly  arrangement 
of  the  parts ;  that  is,  the 
divisions  of  the  calyx 
or  corolla  either  radiate 


FIG.  96.  Begonia  flowers,  monoecious 
A:  a,  staminate  flower;  6,  pistillate  flower.  B,  twisted  stigmas,  enlarged 

from  a  central  axis,  like  the  spokes  of  a  wheel  from  the  hub 
(Fig.  97,  .#),  or  they  are  arranged  with  corresponding  halves  on 
either  side  of  a  central  axis  (Fig.  98,^).  Flowers  on  the  former 
plan  are  said  to  have  radial  symmetry  or  to  be  actinomorphic  (ray- 
shaped),  and  those  on  the  latter  plan  are  said  to  have  bilateral 
symmetry  or  to  be  zygomorphic  (yoke-shaped).  It  is  considered 
that  the  zygomorphic  type  of  flower  is  in  a  general  way  more 
specialized  and  of  a  higher  type  than  the  actinomorphic  one.1 
98.  The  receptacle.2  The  parts  of  the  flower  are  borne  by  the 
more  or  less  enlarged  extremity  of  the  flower  stalk,  which  is 

1  For  illustrations  consult  any  good  modern  flora,  e.g.  Gray's  Manual  of 
Botany,  seventh  edition. 

2  To  THE  TEACHER.  Unless  the  class  is  to  do  a  good  deal  of  work  in  deter- 
mination of  species  of  seed  plants  by  means  of  a  flora,  most  of  Sects.  98-105 
should  be  omitted. 


FLOWERS 


109 


known  as  the  receptacle  shown  in  Fig.  92,  B.  This  varies  much 
in  shape  in  different  kinds  of  flowers,  being  sometimes  nearly 
flat-topped,  as  in  the  lotus  (Nelumbo) ; 
usually  convex,  as  in  the  buttercup, 
raspberry,  and  strawberry;  sometimes 
very  concave  or  even  flask-shaped,  as  in 
the  sweet-scented  shrub  and  the  rose. 
99.  The  perianth. 
The  calyx  and  co- 
rolla taken  together 
are  known  as  the 
perianth.  It  is  con- 
venient to  have  a 
name  which  includes 
them  both,  as  in  many 
flowers,  such  as  those 
of  the  Lily  family,  it 
is  difficult  or  impos- 
sible to  detect  any 
marked  distinctions 
between  sepals  and  petals.  In  most  flowers  the  sepals  are 
green  or  greenish  and  the  petals  of  some  other  color,  ranging 


FIG.  97.  Flowers  of  common  asparagus 

A,  staminate  flower,  with  perfect  stamens  (s)  and 
rudimentary  pistil  (rp) ;  jB,  pistil  late  flower,  with  fully 
developed  pistil  (p)  and  rudimentary  stamens  (rs). 
Such  a  flower  is  practically  unisexual,  but  would 
seem  to  have  become  so  by  descent,  with  modifica- 
tion, from  bisexual  ancestors.  After  H.  Miiller 


W 


FIG,,  98.  Bilaterally  symmetrical 
corolla  of  sweet  pea 

A,  side  view ;  B,  front  view  dissected ; 
s,  standard ;  w,  w,  wings ;  k,  keel 


B 


from  violet  to  red.    There  are,  however,  plenty  of  exceptions 
to  this  rule.   What  are  common  instances  of  such  exceptions  ? 


110 


PRACTICAL  BOTANY 


The  flowers  of  monocotyledons  and  of  dicotyledons  very 
commonly  have  separate  sepals  and  separate  petals  (Fig.  92). 

The  sepals  and  petals  are  then 
said  to  be  distinct.  In  the  more 
specialized  and  higher  families, 
both  of  monocotyledons  and 
of  dicotyledons,  the  receptacle 
often  bears  a  tubular  or  cup- 
like  outgrowth,  and  the  peri- 
anth is  borne  upon  this.  In 
such  cases  the  sepals,  the  pet- 
als, or  both,  appear  as  if  grown 
together  into  a  tube,  upon  the 
free  border  of  which  are  seen 
teeth,  or  lobes,  which  indi- 
cate the  number  of  divisions 
of  which  the  perianth  is  com- 
posed (Fig.  97).1 

Sympetalous  corollas  occur 
of  many  extraordinary  forms, 
enabling  them  to  aid  in  seed 
production.  The  only  such  co- 
rolla shown  in  this  book  is 

Baillon  and  Luerssen  the   fypripedmm  of  the  Orchis 

family  (Figs.  281  and  282). 

100.  Forms  of  the  stamen;  union  of  stamens.  A  common 
form  of  stamen  is  that  shown  in  Fig.  100,  A,  consisting  of  an 
enlarged  portion  called  the  anther,  borne  by  a  slender  stalk 
called  the  filament.  When  the  filament  is  lacking,  the  sta- 
men is  said  to  be  sessile.  Sometimes  the  filaments  appear  to 
be  united,  thus  joining  the  stamens  into  one,  two,  or  more 

1  When  the  sepals  are  distinct  the  flower  is  said  to  be  chorisepalous  (sepa- 
rate sepals)  ;  when  the  petals  are  distinct,  choripetalous.  When  the  sepals 
or  petals  appear  only  as  teeth  or  lobes  on  the  margin  of  a  tubular  or  cup-like 
outgrowth  of  the  receptacle,  the  calyx  is  said  to  be  synsepalous  and  the.  corolla 
sympetalous  (syn  signifies  "  together  ").  The  terms  gamosepalous  and  gamo* 
petalous  are  also  used  (gamos  signifies  ''marriage"  or  "union"). 


FIG.  99.  Diagrams  to  show  struc- 
ture of  an  anther 

A,  younger  stage,  with  four  chambers 
or  locules(loc)  containing  pollen  mother 
cells  dividing  to  form  pollen  grains; 

B,  an  older  stage  in  which  the  pollen 
grains  (p)  are  fully  formed  and  each  pair 
of  locules  is  uniting  to  form  a  pollen  sac, 
which  will  split  open  and  discharge 
along  the  line  of  dehiscence  (d) .  After 


FLOWERS 


111 


groups  (Figs.  Ill  and  121).  In  such  cases  the  stamens  are  said 
to  be  monadelphous,  diadelphous,  triadelphous,  polyadelphous 
(in  one,  two,  three,  many  brotherhoods).  The  function  of  the 
stamen  is  to  produce  pollen,  a  powdery  or  pasty  substance  com- 
posed of  separate  grains  (Figs.  105  and  106),  which  is  formed 
within  four  cavities  in  the  anther  (Fig.  99).  The  two  cavities 
on  each  side  generally  join  to  form  a  single  larger  pollen  sac 
as  the  anther  matures.  Pollen  is  discharged  from  the  mature 
anther  in  various  ways,  as  shown  in  Fig.  100.  The  special 
significance  of  some  of  these  modes  of  discharge  is  explained 
in  Chapter  VIII. 

101.  The  carpel.    The  simplest  form  of  the  organ  which 
bears  ovules  or  rudimentary  seeds  is  called  a  carpel  (from  a 
Greek  word  meaning  "fruit").    The  most  elementary  kind 
of  carpel  is  found  in 

the  lowest  seed  plants, 
and  often  consists,  as 
in  the  pines  and  other 
cone-bearing  trees,  of 
a  single  scale,  with  a 
naked  ovule  borne  at 
its  base  (Fig.  252). 
In  the  higher  seed 
plants  the  carpel  con- 
tains an  ovule-bearing 
cavity  (Figs.  14  and 
101),  in  which  the 
ovules  are  completely 
inclosed  while  they 
are  maturing. 

102.  The  pistil.  The  entire  carpellary  portion  of  the  flower 
of  the  higher  seed  plants  is  called  a  pistil  (Latin  for  pestle).1 
In  flowers  which  have  but  one  carpel,  pistil  and  carpel  mean 

1  It  would  be  better  to  call  it,  as  some  botanists  do,  gynceceum,  but  the 
word  pistil  is  so  much  in  use  in  descriptive  botany  that  it  seems  likely  to  be 
retained  for  a  good  while, 


FIG.  100.  Various  types  of  anther 

A,  iris,  discharging  pollen  by  a  longitudinal  slit; 

B,  barberry,  discharging  pollen  by  uplifted  valves ; 

C,  nightshade;   D,  bilberry,  discharging  pollen 
through  holes  or  pores  at  the  top  of  the  anther. 

A,  B,  C,  after  Baillon ;  Z),  after  Kerner 


112 


PRACTICAL  BOTANY 


the  same  thing,  but  in  flowers  with  two  or  more  carpels,  each 
carpel  is  one  of  the  units  of  which  the  pistil  consists.  A  one- 
carpeled  pistil  is  simple  (Fig.  14),  a  several- 
carpeled  pistil  is  compound  (Figs.  102,  A,  and 
104,  A).  The  parts  usually  found  in  a  pistil 
(Fig.  101)  are  the  ovary,  or  enlarged  ovule- 
bearing  portion,  and  the  style  or  stalk,  on  which 
is  borne  the  stigma,  which  is  usually  expanded, 
knob-like,  or  ridged,  and  with  a  rough  moist 
surface.  When  there  is  no  style  the  stigma  is 
said  to  be  sessile,  and  the  stigma  is  borne  on 
the  ovary. 

A  compound  pistil  may  consist  of  many 
separate  carpels,  as  in  the  stonecrop  (Fig.  92), 
strawberry,  and  buttercup.  Frequently  the 
carpels  are  more  or  less  completely  united 
(Figs.  102,  A,  and  295).  The  ovary  of  a  com- 
pound pistil  may  be  formed  of  the  united 
ovaries  of  the  carpels,  or  a  considerable  part 
of  the  ovary  may  consist  of  a  cup-like  or 
tubular  growth  beneath  the  carpels. 
103.  Locules  of  the  ovary;  placentas.  Compound  "ovaries 
sometimes  have  but  one  ovule-bearing  cavity,  but  more  gener- 
ally they  consist  of  several  separate  chambers,  known  as  loc- 
ules  (Latin,  loculi," little  compartments").  They  are  then  said 
to  be  unilocular,  bi- 
locular,  trilocular, 
and  so  on. 

Ovules  are  not 
borne  by  all  parts 
of  the  interior  of 
the  ovary,  but  are 
usually  produced 
only  along  cer- 
tain regions.  The 
ridge,  column,  or 


ovary 


FIG.  101.  A  pistil, 
with  the  ovary  cut 
through  lengthwise 

stig,  the  stigma 


ABC 

EIG.  102.  Three  modes  of  bearing  ovules 

A,  ovary  three-loculed,  with  the  ovules  borne  on  the 
axis  (central placenta)  formed  by  the  united  partitions ; 
.B,  ovary  one-loculed,  ovules  borne  on  the  ovary  wall 
along  three  placentas ;  (7,  ovary  one-loculed,  ovules 
borne  on  a.  free  central  placenta.  After  Behrens 


FLO  WEES 


113 


other  ovule-bearing  portion  of  the  ovary  is  called  a  placenta. 
Some  common  types  are  shown  in  Fig.  102. 

104.  Superior,  half-inferior,  and  inferior  ovaries.  The  posi- 
tion of  the  ovary  with  reference  to  the  other  whorls  of  the 
flower  is  a  matter  of  great  importance 
in  the  classification  of  plants  and  is 
described  by  the  use  of  appropriate 
names.  When  the  pistil  is  borne  nearer 


FIG.  103.  Part  of  a  flower  cluster  of  evening  primrose 

br,  bracts;  ca,  calyx;  co,  corolla;  ov,  ovary;  p,  pod;  t,  tube  of  perianth, 
appearing  as  if  it  sprung  from  the  tip  of  the  ovary.   Slightly  reduced 

the  extremity  of  the  receptacle  than  any  of  the  other  whorls 
the  ovary  is  said  to  be  superior  (Fig.  93).  When,  however,  the 
end  of  the  floral  axis  is  expanded  in  a  more  or  less  cup- 
shaped  manner,  so  that  the  stamens  (and  the  divisions  of  the 
perianth)  seem  to  spring  from  around  the  ovary,  the  latter 
is  said  to  be  half-inferior.  When  the  concave  floral  axis, 


114  PRACTICAL  BOTANY 

on  the  margin  of  which  the  stamens  are  borne,  appears  to 
be  grown  fast  to  the  ovary,  the  latter  is  said  to  be  inferior^ 
(Fig.  103). 

105.  Floral  diagrams.  Lengthwise  sections  through  the 
flower  greatly  help  the  student  to  understand  its  structure. 
But  still  more  is  to  be  learned  from  a  suitable  cross  section. 
Diagrams  like  those  in  Fig.  104  are  constantly  used  in  flower 
descriptions  to  show  the  relations  of  the  floral  organs.  Such 
a  diagram  is  not  simply  a  sketch  of  the  cut  surfaces  made  by 


BCD 

FIG.  104.  Floral  diagrams 

J,  Lily  family ;  B,  Heath  family ;  C,  Madder  family ;  D,  Composite  family.  The 
dot  above  the  diagram  indicates  the  position  of  the  stem  or  axis  which  bears  the 
flowers.  The  sepals  are  distinguished  from  the  petals  by  being  represented  with 
midribs.  In  B  the  alternate  stamens  are  printed  lighter,  since  some  flowers  of 
this  family  have  five  and  some  ten  stamens.  After  Sachs 

dividing  the  flower  crosswise  near  its  center;  it  is  rather  a 
representation  of  what  would  be  shown  if  all  the  whorls  of 
the  flower  were  brought  into  the  best  position  for  making  a 
characteristic  section,  which  would  pass  through  the  middle 
portions  of  sepals  and  petals  and  through  the  anthers  of  the 
stamens  and  the  ovaries  of  the  carpels.  Note  that  the  sepals 
are  distinguished  from  the  petals  by  being  represented  with 
midribs.  If  any  part  of  the  flower  is  lacking  (as  in  the  case 
of  antherless  stamens,  represented  only  by  filaments),  the 
position  of  the  missing  or  incomplete  organ  may  be  indicated 
by  a  dot. 

1  Often  flowers  with  superior,  half-inferior,  and  inferior  ovaries  are  said 
to  be  respectively  hypogynous,  perigynous,  and  epigynous. 


CHAPTER  VIII 


POLLINATION  AND  FERTILIZATION 

106.  Pollination.    By  the  term  pollination  the  conveyance 
of  pollen  to  the  pistil  is  meant.    Some  of  the  various  means 
by  which  this  result  is  secured  are  discussed  later  on  in  the 
^  present  chapter.    In  whatever  way 

fl% i     A  the  pollen  is  carried  from  the  sta- 

mens to  the  pistil  (usually  by  the 
wind,  by  ani- 

B       ^ss^  JT~  >  L       mals,    or    by 

contact  of  the 
anthers  with 
the  stigma), 


FIG.  105.  Types  of  pollen  grains 

A,  dandelion ;  B,  hemp ;  C,  gentian ; 

D,  squash.   All  greatly  magnified. 

After  Kerner 


FIG.  106.  Types  of  pollen  grains 

A,  evening  primrose,  the  grains  united 

by  sticky  threads;  B,  marsh  mallow. 

Greatly  magnified.   After  Kerner 


its  lodging  place  in  the  higher  seed  plants  is  on  the  stigma. 

This  generally  has  a  rough,  often  moist  and  sticky  surface. 

107.  The  pollen  grain  and  its  germination.1  Pollen  grains  are 

of  many  forms,  a  few  of  which  are  shown  in  Figs.  105  and  106. 

1  The  logical  order  of  treatment  would  be  to  say  all  that  is  to  be  said 
about  pollination  before  dealing  with  its  result,  fertilization.  It  is,  however, 
more  convenient  to  discuss  the  minute  structure  of  pollen  and  the  pistil  soon 
after  Chapter  VII  is  completed,  and  then  to  give  details  of  some  of  the 
modes  by  which  pollination  is  secured. 

116 


116 


PRACTICAL  BOTANY 


Each  mature  grain  contains  a  generative  nucleus  and  a  tube 
nucleus  (g  and  £,  Fig.  107,  A).    After  the  pollen  grain  lodges 
on  the  stigma  the  inner  coat  of  the  grain 
becomes  slightly  distended  by  osmosis,  pro- 
duced by  contact  with  the  moist  stigmatic 
surface.    The  distention  of  the  inner  coat 
causes  it  to  protrude  through  the  outer  coat 
and  it  at  length  develops  into  the  wall  of 
a  pollen  tube  (Fig.  107).    This  tube  has  the 
nucleus  (T)  at  its 
tip  and  a  generative 
cell  (#)  somewhere 
within   the  tube. 
Finally  the  genera- 
tive cell  divides  in- 
to two  male  nuclei, 
these  develop  into 
male  cells  (Fig.  10  7, 
Z?) ,  and  the  tube  nu- 
cleus disappears. 

108.  Course  of  the 
pollen  tube:  fertilization. 
The  pollen  tube  makes  its 
way  from  the  stigma  to 
the  ovary  either  through 
a  canal  or  passage  (Fig. 
108),  or  by  directly  trav- 
ersing the  cellular  tis- 
sue of  the  style,  upon 
which  it  acts  so  as  to  eat 
its  way  along  by  means 


FIG.  107.  Germination  of  the  pollen  grain 
of  a  dicotyledon 

J,  an  early  stage  in  the  germination ;  7?,  later 
stage,  with  the  tube  rather  fully  developed ; 
<7,  generative  cell ;  t,  tube  nucleus ;  Sj,  s2,  male 
cells  formed  from  the  generative  cell.  It  is  ap- 


parent that  when  the  growth  of  the  tube  is  far 

advanced  the  tube  nucleus  (t)  almost  disappears. 

Much  magnified.  After  Bonnier  and  Sablon 


of  ferments  (Sect.   36) 

secreted   by    the    tube. 

The  tube    may  require 

a  day  or  more  to  reach  the  ovule.    Food  materials  from  the 

style  are  dissolved  by  the  enzymes  and  used  in  promoting  the 


POLLINATION  AND  FERTILIZATION 


117 


growth  of  the  pollen  tube.1   When  the  tip  of  the  tube  reaches 
the  ovary  it  usually  penetrates  to  the  interior  of  an  ovule  by 


FIG.  108.  Pollen  grains  produc- 
ing tubes,  on  stigma  of  a  lily. 
Much  magnified 

<7,  pollen  grains ;  t,  pollen  tubes ; 

p,  papillae  of  stigma ;  c,  canal  or 

passage  running  toward  ovary 

means  of  the  little  opening 
(micropyle)  at  one  end  of  the 
ovule  (Fig.  109).2  One  of  the 
male  cells  now  unites  with 


FIG.  109.  Diagram  to  illustrate  course 
of  the  pollen  tube  during  fertilization 

p,  pollen  grains ;  t,  pollen  tube ;  n,  nucel- 
lus,  or  body  of  the  ovule ;  a,  antipodal 
cells  of  embryo  sac ;  en,  endosperm  nu- 
cleus of  embryo  sac ;  egg,  the  egg  ap- 
paratus, consisting  of  the  egg  cell  and 
two  cooperating  cells ;  m,  the  mi?ropyle, 
or  small  opening  through  which,  in  most 
ordinary  flowering  plants,  the  pollen 
tube  makes  its  way  to  the  egg  at  the  tip 
of  the  embryo  sac 


the  egg  nucleus  of  the  ovule. 
The    other  male    cell   in  many   cases  unites  with  the  cen- 
tral nucleus  of  the  embryo  sac  to  form  the  endosperm  nucleus 

1  See  Green,  Vegetable  Physiology,  chap.  xxvi.   P.  Blakiston's  Son  &  Co., 
Philadelphia. 

2  In  some  plants  the  tube  makes  its  way  directly  through  the  tissue  of 
the  ovule. 


118  PKACTICAL  BOTANY 

(Fig.  265).  The  result  of  fertilization  is  to  cause  the  egg  of 
the  ovule  to  develop  into  an  embryo.  One  of  the  first  steps 
of  embryo  formation  is  shown  in  Fig.  267.  The  fertilization  of 
the  egg  within  the  ovule  may  result  from  the  proper  placing 
of  a  single  pollen  grain,  but  the  result  is  more  certain  if  there 
are  several  grains. 

109.  Advantages  of  reproduction  by  seed.    As  has  already 
been  shown  (Sects.  33  and  75-80),  reproduction  may  readily 
be  accomplished  by  buds  produced  on  roots,  stems,  or  leaves, 
—  vegetative  reproduction.   This  method  is  much  quicker  than 
that  by  the  agency  of  seed,  as  is  well  shown  in  the  case  of 
the  potato.    It  would  seem  that  sexual  reproduction,  repro- 
duction by  means  of  seed,  a  more  complicated  process,  would 
hardly  have  originated  unless  on  the  whole  it  were  of  advan- 
tage to  plants.1    It  is  evidently  desirable  for  the  continuation 
of  the  various  kinds  of  plants  to  have  such  a  comparatively 
portable,  heat-,  cold-,  and  drought-resisting  structure  as  the 
seed  to  disseminate  plants  over  large  areas  and  to  maintain 
plant  life  under  unfavorable  conditions.    But  some  botanists 
have  been  led  to  think  also  that  sexual  reproduction  is  of 
distinct  advantage  to  plants  by  giving  them  greater  vigor 
than  is  secured  by  long-continued  vegetative  reproduction,  as 
in  the  case  of  potatoes  grown  for  years  by  planting  the  tubers. 
It  is  also  of  advantage  to  the  plant  to  reproduce  by  means  of 
seed,  because  this  secures  variations  in  the  offspring  which 
may  result  in  greater  fitness  to  meet  the  conditions  of  its 
existence  (Chapter  XXIII). 

110.  Ecology.  Plant  ecology  (from  two  Greek  words  meaning 
"house"  and  "discourse")  is  the  subdivision  of  botany  which 
discusses  the  relations  of  the  plant  to  its  surroundings.   Defin- 
ing the  subject  more  in  detail,  it  may  be  said  that  ecological 
botany  treats  of  the  effects  upon  plants  of  the  various  forces 
and  forms  of  energy,  —  such  as  gravity,  heat,  light,  electricity, 
currents  of  air  and  water,  —  as  well  as  of  the  effects  of  chemi- 
cal elements  and  compounds.    It  also  comprises  the  study  of 

1  For  a  brief  account  of  the  beginnings  of  sex  in  plants  see  Chapter  XIII. 


POLLINATION  AND  FERTILIZATION 


119 


the  social  relations  between  plants  and  other  injurious  or  help- 
ful plants  and  animals.1 

The  ecology  of  flowers  is  largely  concerned  with  the  ways  in 
which  pollination  is  brought  about.2   This  subject  is  of  suffi- 
cient importance  to  have    accumulated  an 
extensive    literature,   the   principal   treatise 
upon  it  being  Knuth's  "Bliithenbiologie,"  em- 
bracing nearly  three  thousand  pages.    There 
is  also  an  excellent  English  translation  of 
this  remarkable  book.3 

111.  Pollination  and  floral  characteristics. 
Some  of  the  most  obvious  divisions  of  flowers 
into  everyday  groups,  such  as  are  made  by 
children  and  other  unscientific  people,  are 
those  into  scented  and  scentless,  showy  and 
inconspicuous  kinds.  Another  less  obvious 
but  important  distinction  is  based  on  the 
presence  or  absence  of  the  sweet  liquid  (com- 
monly called  honey,  but  more  properly  known 
as  nectar)  so  familiar  at  the  tips  of  colum- 
bine spurs  and  in  clover  and  honeysuckle 
blossoms.  Such  characteristics  as  those  just 
mentioned  have  much  to  do  with  the  way  in 
which  flowers  have  their  pollen  transferred 
from  anthers  to  stigma. 

Flowers  with  feathery  stigmas  (Fig.  110) 
and  dry,  dust-like  pollen  are  usually  polli- 
nated by  the  wind. 

Flowers  with  stigmas  which,  before  they  wither,  curve  so 
as  to  bring  the  anthers  into  contact  with  the  stigma  (Fig.  Ill) 
are  usually  self-pollinated. 

1  A  great  deal  of  what  was  said  about  the  behavior  of  roots,  stems,  and 
leaves  in  Chapters  III- VI  is  to  be  classed  as  plant  ecology,  though  it  was 
not  given  a  separate  name  in  those  chapters. 

2  See  Kerner-Oliver,  Natural  History  of  Plants,  Vol.  II.  Henry  Holt  and 
Company,  New  York. 

8  Knuth-Davis,  Handbook  of  Flower  Pollination.  Clarendon  Press,  Oxford. 


FIG.  110.  Pistil  of 
timothy  with  feath- 
ery stigmas 

sti,  stigmas.    Mag- 
nified about  twenty 
times 


120  PEACTICAL  BOTANY 

Flowers  of  any  other  color  than  green,  or  which  are  fragrant, 
have  nectar,  or  show  marked  deviations  from  radial  sym- 
metry (Figs.  98  and  281),  are  generally  more  or  less  wholly 
dependent  upon  animals  (commonly  insects  of  some  kind)  for 
pollination.1 

112.  Wind-pollinated  flowers.  The  number  of  plants  which 
depend  upon  the  transference  of  pollen  by  the  wind  is  very 
great,  embracing  as  it  does  large  families,  such  as  that  of  the 
cone-bearing  trees  (Pine  family),  the  grasses,  and  the  sedges. 

It  is  easy  to  see  that  pollen-carrying  by  the  wind  must  be 
a  very  wasteful  process,  since  only  now  and  then  a  pollen 
grain  is  likely  to  alight  on  a  stigma  of  the  species  of  plant 
which  produced  it.  Accordingly,  flowers  which  have  their  pol- 
len carried  by  the  wind  yield  it  in  enormous  quantities.  It  is 
estimated  that  a  medium-sized  plant  of  Indian  corn  produces 
about  50,000,000  pollen  grains ;  a  pine  tree  must  produce  an 
unimaginably  great  number.  The  stigmas  of  wind-pollinated 
flowers  which  catch  the  dust-like  flying  pollen  are  brush-like,  as 
in  the  hazels ;  feathery,  as  in  most  grasses  (Fig.  110);  or  pro- 
longed and  thread-like,  as  in  Indian  corn  (Fig.  336).  Wind- 
pollinated  flowers  frequently  appear  before  the  leaves  of  the 
plant  which  bears  them.  What  advantage  is  there  in  this  ? 

113.  Self-pollinated  flowers.  As  a  rule,  inconspicuous  flowers 
with  moist,  sticky  pollen  are  wholly  self -pollinated  or  can  pol- 
linate their  own  stigmas  when  pollen  from  another  flower 
is  not  supplied  to  them.    Familiar  examples  of  such  flowers 
are  pigweeds,2  knotgrass,3  the  common  chickweed,4  the  round- 
leaved  mallow5  (Fig.  Ill),  the  low  cudweed,6  and  the  com- 
mon groundsel.7    It  is  not  infrequently  the  case  that  flowers^ 
when  they  first  mature,,  have  the  anthers  and  the  stigma  far 
enough  apart  to  make  it  impossible  for  pollen  to  lodge  upon 

1  See  Bergen  and  Davis,  Laboratory  and  Field  Manual  of  Botany,  Sect.  149. 
Ginn  and  Company,  Boston. 

2  Chenopodium,  various  species.  6  Malva  rotundifolia. 

8  Polygonum  amculare.  6  Gnaphalium  uliginosum. 

*  Stellaria  media.  7  Senecio  vulgaris. 


POLLINATION  AND  FERTILIZATION 


121 


the  stigma  as  long  as  the  flower  remains  undisturbed ;  but  at 
a  later  period  in  the  development  of  the  organs,  anthers  and 
stigmas  may  grow  into  contact  with  each  other  and  self-polli- 
nation be  secured  (Fig.  111). 

It  is  a  remarkable  fact  that  when  a  stigma  is  pollinated 
with  pollen  from  the  same  flower  or  from  another  flower  of 
the  same  plant,  and  also  with  pollen  from  another  individual 
of  the  same  kind,  generally  only  the  latter 
pollen  takes  effect  in  fertilizing  the  egg.   In 
other  words,  foreign  pollen  is  prepotent  over 
pollen  from  the  same  individual.1 

114.  Self-pollination  and  cross-pollination. 
The  process  of  self-pollination  is  usually 
rather  simple,  as  may  have  been  inferred 
from  Sect.  108.  Not  infrequently  the  be- 
ginner in  botany  may  be  led  to  wonder 
whether  it  would  not  be  advantageous  to 
the  plant  world  if  all  flowers  were  bisexual 
and  pollinated  their  own  pistils.  The  matter 
is  not,  however,  quite  as  simple  as  it  ap- 
pears to  be.  The  earliest  seed  plants  were 
doubtless  remotely  related  to  our  evergreen 
cone-bearing  trees  of  to-day  (such  as  pines, 
spruces,  and  cedars),  and  these  cone-bearers 
have  unisexual  flowers  (Figs.  251  and  262) 
and  are  wind-pollinated.  Bisexual  flowers  came  later.  It  is  likely 
that,  later  still,  plants  with  unisexual  flowers  have  come  into 
existence  by  descent,  with  gradual  modifications,  from  ancestors 
which  bore  bisexual  flowers.  One  proof  of  this  is  drawn  from 
the  fact  that  there  are  many  cases  of  flowers  which  are  practi- 
cally unisexual  but  show  rudimentary  pistils  in  the  staminate 
flowers  and  rudimentary  stamens  in  the  pistillate  ones,  as  in 
the  common  asparagus  (Fig.  97).  Occasionally  the  asparagus 
has  perfect  stamens  and  pistils  in  the  same  flower. 

1  See  Darwin,  Cross  and  Self  Fertilisation  in  the  Vegetable  Kingdom, 
chap.  x.   D.  Appleton  and  Company,  New  York. 


FIG.  111.    Stamens 
and  pistils  of  round- 
leaved  mallow 

The  flower  has  heen 
open  for  a  consider- 
able time,  and  the 
stigmas  have  curved 
so  as  to  come  into 
contact  with  the  sta- 
mens and  insure  self- 
pollination.  AfterH. 
Miiller 


122  PRACTICAL  BOTANY 

By  cross-pollination  is  meant  the  process  of  transferring  for- 
eign pollen  to  the  stigma.  The  effect  in  fertilization  is  the 
same  whether  the  pollen  is  carried  by  the  wind  or  otherwise. 

115.  Advantages  of  cross-pollination.  As  already  stated 
(Sect.  113),  foreign  pollen  is  usually  more  effective  than  the 
pollen  from  the  same  individual.  Charles  Darwin,  the  great 
English  naturalist,  showed  by  experiments  continued  through 
eleven  years  that  in  many  cases  the  plant  derives  great  advan- 
tages from  cross-pollination.1  He  found  that  in  plants  the 
flowers  of  which  are  not  especially  suited  to  self-pollination 
if  left  to  themselves,  but  which  he  pollinated  thoroughly  by 
hand,  the  plants  grown  from  the  seeds  of  cross-pollinated 
flowers  usually  much  exceeded  in  height,  weight,  and  fertil- 
ity those  from  self-pollinated  flowers.  It  was  found,  for  in- 
stance, that  when  the  yellow  monkey  flower  (Mimulus  luteus) 
was  self-pollinated  to  the  ninth  generation  the  plants  thus 
produced  were  -ffa  the  height  of  plants  which  came  from 
those  self-pollinated  to  the  eighth  generation  and  then  cross* 
pollinated  with  a  plant  of  another  stock.  In  fertility  the  two 
kinds  (self-pollinated  to  the  ninth  generation  and  cross-polli- 
nated at  the  end  of  the  eighth  generation)  were  in  the  ratio  T-|^. 

Cabbages  were  raised  by  Darwin  from  seeds  of  a  third 
self-pollinated  generation  and  also  from  those  of  the  second 
self-pollinated  generation  crossed  with  a  plant  from  a  distant 
garden.  The  self -pollinated  cabbages  were  only  -ffo  the  weight 
of  the  cross-pollinated  ones.  These  two  examples  may  serve  as 
extreme  instances  of  the  benefits  of  cross-pollination.  In  many 
cases  less  advantage  is  gained  by  it,  and  there  is  a  considerable 
group  of  plants  which  seem  to  be  indifferent  to  the  source  from 
which  the  pollen  comes,  that  from  the  same  flower  answering 
as  well  as  that  from  another  individual  of  the  same  species. 
The  practical  value  of  a  knowledge  of  the  effects  of  different 
kinds  of  pollination  is  often  very  great  (Chapter  XXIII). 

1  See  Darwin,  The  Effects  of  Cross  and  Self  Fertilisation  in  the  Vegetable 
Kingdom,  chaps,  i  and  vii-ix.  D.  Appleton  and  Company,  New  York.  For 
facts  about  flowers  which  do  not  need  cross-pollination  see  Sects.  121  and  126. 


POLLINATION  AND  FERTILIZATION 


123 


-ti 


116.  Insects  as  carriers  of  pollen.  Most  flowers  which  re- 
quire or  are  benefited  by  cross-pollination  and  which  are  not 

wind-pollinated  depend  upon 
insects  as  pollen  carriers.  It  is 
not  an  overstatement  to  say 
that,  in  general,  flowers  seem 
to  have  acquired  their  colors 
(other  than  green)  and  their 
odors  as  means  of  attracting 
the  attention  of  insects  which 
may  serve  to  cross-pollinate 
them.  Insects  vary  greatly  in 
their  efficiency  as  pollinators, 
the  small  ones  with  smooth  sur- 
faces on  the  head,  legs,  and  ab- 
domen, such  as  ants  and  many 
beetles,  carrying  little  pollen, 
while  bees, 
moths,  and 

butterflies  often  carry  considerable  quan- 
tities. Many  bees  in  particular  are  provided 
with  a  special  collecting  apparatus  for 
pollen  (Figs.  112  and  113).  Although  the 
portion  which  they  carry  to  the  hive  or  nest 
for  food  is  of  no  use  for  pollination,  much 
of  that  which  is  smeared  over  the  general 
surface  of  the  body  serves  to  pollinate  the 
stigmas  of  flowers  which  they  afterwards 

.  . ,       A  -,  , .     -,  .,,  , .          *  ,,         FIG.  113.    Right  hind 

visit.  A  good  practical  illustration  of  the  leg  of  a  bee  $acropis) 
importance  of  insect  visits  is  afforded  by  Thetibiaiscoveredwith 
the  case  of  cucumbers  grown  in  winter  pollen  of  the  common 
under  glass.  It  is  found  necessary  to  keep  loos™£^  S^' 
hives  of  bees  in  the  cucumber  houses  in 
order  to  insure  pollination  and  consequent  crops  of  cucumbers. 
Some  idea  of  the  number  of  insect  visits  may  be  gathered 
from  the  fact  that  in  a  single  locality  dandelion  flowers  have 


FIG.  112.  Pollen-carrying  apparatus 
of  leg  of  honeybee 

A,  right  hind  leg  of  a  honeybee  (seen 
from  behind  and  within) ;  B,  the  tibia 
(ti),  seen  from  the  outside,  showing  the 
collecting  basket  formed  of  stiff  hairs. 
After  H.  Miiller 


124 


PKACTICAL  BOTANY 


been  seen  to  be  frequented  by  100  kinds  of  insects.1  The  sta- 
tistics of  visitors  to  the  flowers  of  yarrow,  Canada  thistle,  and 
the  willows  are  fully  as  remarkable. 

117.  Attractions  offered  by  insect-pollinated  flowers.  Insects 
are  led  to  visit  flowers  for  the  sake  of  procuring  food.   This  is 
usually  either  pollen — as  in  the  flowers  of  many  species  of 

meadow  rue,  Clematis,  Anemone, 
poppy,  rose,  Spiraea,  and  St- 
John's-wort  —  or  both  pollen 
and  nectar,  as  in  most  kinds 
of  conspicuous  flowers. 

Nectar  is  usually  secreted 
by  nectar  glands,  small  organs 
which  are  often  to  be  found 
near  the  base  of  the  flower, 
as  in  buckwheat  (Fig.  114). 
Sometimes  the  nectar  remains 
on  the  surfaces  of  the  glands, 
sometimes  it  trickles  down  into 
the  bottom  of  the  flower,  and 
sometimes  —  as  in  the  columbine  and  the  honeysuckle  —  it 
is  stored  in  pouches  called  nectaries,  situated  at  the  bases  of 
separate  petals  or  at  the  bottom  of  the  sympetalous  corolla. 

Honey  is  nectar  which  has  been  swallowed  by  the  bee  and, 
by  partial  digestion  in  its  crop,  has  undergone  slight  chemical 
changes. 

118.  Odors  of  flowers  as  attractions  to  insects.  It  is  evident 
from  familiar  facts  that  many  insects  have  an  acute  sense  of 
smell.    The  way  in  which  flies  are  attracted  by  decaying  meat 
or  fish,  and  bees  and  wasps  by  a  cider  press  at  work,  or  by 
fruit-preserving  operations,  is  a  matter  of  common  observa- 
tion.   A  single  cluster  of  carrion-scented  flowers  has  been 
known  to  attract  carrion  flies  and  dung  beetles  from  a  distance 
of  hundreds  of  yards.    Some  flowers  —  such  as  those  of  the 


FIG.  114.  Flower  of  buckwheat 

Lengthwise  section,  showing  nectar 
glands  n.  Five  anthers  are  discharg- 
ing pollen ;  the  other  three  here  shown 
are  not  quite  mature.  After  H.  Miiller 


1  See  Knuth-Davis,  Handbook  of  Flower  Pollination,  Vol,  II.   Clarendon 
Press,  Oxford. 


POLLINATION  AND  FERTILIZATION  125 

\7irginia  creeper  (Psedera),  the  Dutchnian's-pipe,  the  blueber- 
ries, and  many  others  —  are  so  inconspicuous  that  apparently 
their  numerous  insect  visitors  must  be  attracted  by  an  odor 
which  is  almost  or  quite  imperceptible  to  us. 

It  seems  certain  that  the  odors  of  flowers  have  been  devel- 
oped with  reference  to  the  sense  of  smell  in  animals  (usually 
insects),  and  that  these  odors  serve  as  a  most  efficient  means 
of  insuring  insect  visits. 

It  is  a  most  interesting  fact  that  many  flowers  give  off  their 
scent  mainly  at  the  time  of  day  when  the  insects  which  polli- 
nate them  are  most  active.  Thus  some  catchflies,  the  petu- 
nias, some  kinds  of  tobacco,  and  several  honeysuckles  have 
little  odor  by  day,  but  are  very  fragrant  at  night  when  the 
moths  which  pollinate  them  are  on  the  wing.  On  the  other 
hand,  many  plants  of  the  Pea  family,  which  are  pollinated  by 
day-flying  bees  and  butterflies,  give  off  their  scent  mostly  by 
day,  and  especially  in  strong  sunshine. 

119.  Colors  of  flowers  as  attractions  to  insects.  There  has 
been  much  discussion  among  botanists  as  to  how  far  insects  are 
led  to  visit  flowers  by  displays  of  color.  It  appears  to  be  fairly 
certain  that  no  insects  can  make  out  the  forms  and  sizes  of 
objects  at  a  distance  of  more  than  six  feet,  and  that  many  are 
unable  to  see  clearly  even  two  feet.1  In  spite  of  this,  however, 
it  seems  probable  that  the  colors  of  flowers  are  an  important 
means  of  attraction  for  many  flower-frequenting  insects.2 

The  commonest  method  of  color  display  is  that  in  which  the 
color  (other  than  green)  is  mainly  found  in  the  corolla,  as  in 
the  flowers  of  the  poppy,  rose,  sweet  pea,  and  morning-glory. 
Sometimes  the  calyx  also  is  bright-colored,  or,  as  in  the  Hepat- 
ica,  the  Anemone,  and  the  Clematis,  the  corolla  is  wanting  and 
the  showy  calyx  looks  like  a  corolla.  Not  infrequently  the 

1  See  Packard,  Text-Book  of  Entomology.    The  Macmillan  Company, 
New  York. 

2  See  Kerner-Oliver,  Natural  History  of  Plants,  Vol.  II.    Henry  Holt  and 
Company,  New  York.  Also  Knuth-Davis,  Handbook  of  Flower  Pollination, 
Vol.  I ;  and  Andreae,  Inwief  ern  werden  Insekten  durch  Farbe  und  Duft  der 
Blumen  angezogen,  Beiheft,  Bot.  Centralblatt,  15,  1903,  pp.  427-470. 


126 


PRACTICAL  BOTANY 


display  is  all  made  by  an  enlarged  and  conspicuous  set  of 
specialized  leaves  (bracts)  which  surround  the  flower,  as  in 
the  flowering  dogwood  and  many  euphorbias  (Fig.  292),  or 
even  by  highly  colored  ordinary  leaves,  as  in  the  poinsettia. 
120.  Degrees  of  specialization  for  insect  visitors.  Flowers 
with  a  spreading  perianth  and  radial  symmetry  —  like  those 
of  the  stonecrop  (Fig.  92)  and  the  live-forever,  the  buckwheat 
(Fig.  114)  and  the  caraway  (Fig.  295),  buttercups,  poppies, 

roses,  and  hun- 
dreds of  other 
familiar  kinds — 
are  open  to  all 
comers,  and  are 
frequented  by 
many  sorts  of  in- 
sects, from  flies 
to  bees. 

Flowers  with 
bilateral  symme- 
try —  like  vio- 
lets, wild  balsam 
(Fig.  119),  most 
flowers  of  the 
Pea  family  (Fig.  98),  mints,  and  many  others  —  are  usually 
not  suited  to  indiscriminate  visitors,  but  only  to  those  insects 
which  can  get  at  the  nectar,  the  pollen,  or  both.  In  violets,  for 
example,  the  pollen  is  abundant,  but  is  concealed  within  the 
throat  of  the  corolla,  and  the  nectar  is  deep  down  in  the  spur 
of  the  corolla.  Both  pollen  and  nectar  are  easily  reached  by 
the  tongues  of  bees,  but  not  by  small  insects.  In  the  snap- 
dragon the  mouth  of  the  corolla  is  firmly  closed,  so  that  small 
insects  cannot  enter  it.  Larger  ones,  such  as  bees,  can,  how- 
ever, readily  overcome  the  elasticity  of  the  hinge  at  the  junc- 
tion of  the  lips  and  enter  the  flower  (Fig.  115). 

There  are  some  flowers  which  appear  to  be  dependent  on 
pollination  by  a  single  kind  of  insect  only,  and  therefore  are 


FIG.  115.  Flowers  of  snapdragon 

A,  with  lips  of  corolla  tightly  closed ;  JB,  with  the  lips 
forced  open  by  a  visiting  bee 


POLLINATION  AND  FERTILIZATION  127 

unable  to  set  any  seeds  if  that  species  of  insect  is  not  at  hand 
to  carry  their  pollen.  One  famous  example  of  this  depend- 
ence of  the  flower  on  a  particular  insect  is  that  of  the  common 
fig,  which  may  bear  large  and  juicy  fruits  without  insect  visits, 
but  cannot  produce  seed  that  will  grow  without  being  polli- 
nated by  a  small  species  of  wasp.  Another  instance  is  that  of 
the  yuccas  (Sect.  121). 

121.  Pollination  in  yucca.  The  yuccas  are  mainly  plants  of 
desert  or  semi-desert  regions,  especially  characteristic  of  the 
southwestern  United  States  and  Mexico.  One  species,  the 
Adam's-needle,  or  Spanish  dagger,  is  a  native  of  the  Atlan- 
tic and  Gulf  coast,  and  commonly  cultivated.  The  flowers 
of  yuccas  are  white  or  nearly  so,  mostly  with  large  spreading 
corollas,  and  borne  in  great  clusters,  of  one  of  which  Fig.  116 
represents  only  a  small  portion.  The  stamens  are  somewhat 
shorter  than  the  carpels,  with  abundant  sticky  pollen,  and  the 
pistil  consists  of  three  carpels  which  are  joined  to  form  a  tube, 
which  is  stigmatic  on  its  inner  surface.  Pollination  is  impos- 
sible without  insect  aid,  and  this  is  furnished  by  a  small  moth 
(Pronuba).  Unlike  most  cases  of  insect-pollination,  that  per- 
formed by  the  yucca  moth  is  self-pollination. 

The  flowers  of  yucca  are  fully  open  and  in  condition  for 
pollination  during  only  a  short  period.  Throughout  the  day 
the  female  moth  remains  at  rest  within  the  flower,  almost  hid- 
den by  the  stamens  (Fig.  116).  At  dusk  she  begins  active 
work,  first  crawling  to  the  anthers,  on  the  surfaces  of  which 
the  pollen  generally  remains  in  a  lump  after  its  expulsion 
from  the  pollen  sacs.  She  collects  pollen  into  a  mass,  held  as 
shown  in  Fig.  117,  which  is  sometimes  three  times  the  size  of 
her  head.  She  then  crawls  over  or  within  the  flower,  with 
occasional  sudden  starts,  until  finally  she  takes  a  position 
astride  of  one  stamen  and  with  her  head  toward  the  stigma, 
as  shown  in  the  top  flower  of  Fig.  116.  Lowering  the  abdo- 
men between  the  stamens,  she  now  thrusts  the  sharp  tip  of 
the  egg-depositing  apparatus  (ovipositor)  into  the  soft  ovary 
wall  and  inserts  an  egg  into  an  ovule.  After  depositing  an  egg, 


FIG.  116.  Flowers  of  yucca  visited  by  the  moth  Pronuba 

The  work  of  the  moth  is  suggested  by  its  position  in  the  several  flowers.   In  the 
first  flower  (the  lowest),  the  moth  is  gathering  pollen ;  in  the  second,  she  is  polli- 
nating the  stigma ;  in  the  third,  she  is  in  the  position  of  rest  during  the  day ;  in 
the  fourth,  in  the  position  of  rest  when  disturbed ;  in  the  fifth,  ovipositing 

128 


POLLINATION  AND  FERTILIZATION 


129 


FIG.  117.  Head  of  Pronuba 
moth.    Magnified 

p,  mass  of  pollen  held  in  posi- 
tion hy  spinous  appendages  of 
the  moth's  head 


the  moth  runs  to  the  top  of  the  pistil,  as  shown  in  Fig.  116, 
uncoils  the   organs  which  hold  the  pollen  mass,  and  with 

her  tongue  tlirusts  the  pollen  vigor- 
ously into  the  stigmatic  opening  for 
several  seconds.  As  the  stigma  is 
usually  pollinated  after  every  depo- 
sition of  an  egg,  in  cases  where  ten 
or  a  dozen  eggs  are  introduced  into  a 
single  pistil  it  is  pollinated  as  many 
times.  After  the  hatching  of  the 
eggs,  each  little  grub  that  is  pro- 
duced from  them  eats  up  the  ovule  in 
which 
it  was 
depos- 
ited, leaving,  however,  many 
other  ovules  to  mature  into 
seeds.  It  then  bores  its  way  out 
through  the  capsule,  drops  to 
the  earth,  and  makes  a  cocoon  of 
silk  a  few  inches  underground. 
It  probably  does  not  assume  the 
form  of  the  adult  (winged)  in- 
sect until  near  the  next  bloom- 
ing time  of  the  yuccas. 

The  relations  of  the  yucca 
moth  to  the  plant  afford  a  most 
remarkable  example  of  cooper- 
ation between  a  plant  and  one 
of  the  lower  animals.  Without 
pollination  by  the  moth,  yuccas 
produce  no  seeds,  while,  on  the  other  hand,  without  yucca 
capsules  and  their  contents  the  larvae  hatched  from  the  eggs 
of  the  moth  would  starve.1 

1  See  Proceedings  of  the  American  Association  for  the  Advancement  oj 
Science,  1880,  Vol.  XXIX,  paper  entitled  "  Further  Notes  on  the  Pollination 


FIG.  118.  Pod  of  a  tree  yucca 

p,  perforations  caused  by  escape  of 
larva  of  yucca  moth.  Somewhat 
reduced.  After  Thirteenth  Annual 
Report  of  Missouri  Botanical  Garden 


130 


PRACTICAL  BOTANY 


122.  Bird-pollinated  and  snail-pollinated  flowers.  Although 
by  far  the  greater  part  of  the  pollination  done  by  animals  is 
due  to  insects,  birds  also  perform  this  office  for  many  flowers. 
Those  which  are  most  efficient  in  this  work  are  the  sunbirds 
of  Asia,  Africa,  and  other  hot  countries,  and  our  own  humming 
birds.  Most  bird-pollinated  flowers  are  large  and  showy,  many 
of  them  scarlet  or  deep  orange  in  color.  Among  the  most  famil- 
iar of  our  wild 
flowers  much 
visited  by  hum- 
ming birds  are 
the  wild  balsam 
or  jewelweed 
(Fig.  119),  the 
trumpet  creeper, 
and  the  cardinal 
flower ;  among 
cultivated  ones 
are  the  scarlet 
salvia,  the  gla- 
diolus, and  the 
trumpet  honey- 
suckle.1 

Snails  are  not  so  abundant  in  most  parts  of  our  own  country 
as  to  be  important  agents  in  pollinating  flowers,  but  in  some 
parts  of  Europe  they  swarm  in  almost  countless  numbers  on 
the  foliage  and  the  flowers  of  many  species  of  plants,  and  are 
known  to  pollinate  some  flowers,  particularly  those  of  the 
Arum  family,  related  to  our  jack-in-the-pulpit  and  dragon- 
root  (Fig.  277). 

of  Yucca,  and  on  Pronuba  and  Prodoxus,"  by  C.  V.  Riley ;  also  the  same 
reprinted  as  a  pamphlet  by  the  Missouri  Botanical  Garden,  1883.  See  also 
the  Thirteenth  Annual  Report  of  the  Missouri  Botanical  Garden,  1902,  paper 
entitled  <f  The  Yuccese,"  by  William  Trelease. 

1  Other  flowers  are  the  buckeye,  horse-chestnut,  canna,  century  plant, 
cotton,  evening  primrose,  milkweed  (Asclepias),  oleander,  painted  cup, 
petunia,  tobacco. 


FIG.  119.  Wild  balsam  (Impatiens  biflora) 
The  spurred  flowers  are  much  visited  by  humming  birds 


POLLINATION  AND  FERTILIZATION 


131 


123.  Prevention  of  self-pollination,  dichogamy.  Of  course 
dioecious  flowers  like  those  of  the  willow  cannot  be  self-polli- 
nated. Monoecious  ones  like  those  of  Indian  corn  (Figs.  335 
and  336)  are  likely  to  be  pollinated  with  pollen  from  another 
plant.  As  regards  bisexual  flowers,  it  is  evident  that  there 
are  many  opportunities  for  self-pollination.  But  in  all  cases  in 
which  cross-pollination  produces  more  seed  or  stronger  plants, 

or  both,  it  is  clear  that  any- 
thing in  the  structure  or  mode 
of  development  of  the  flower 


FIG.  120.  Dichogamous  flowers  of 
plantain  (Plantago  lanceolata) 

A,  earlier  stage,  pistil  mature,  stamens 

not  yet  appearing  outside  the  corolla ; 

J3,  later  stage,  pistil  withered,  stamens 

mature.   Six  times  natural  size 


FIG.  121.  Dichogamy  in  the 
high  mallow 

In  A  the  stamens  are  mature  but 
the  stigmas  are  pressed  together 
into  a  club-shaped  mass  (hidden 
by  the  numerous  stamens).  InJB 
the  anthers  are  withered  and  the 
stamens  droop,  while  the  stigmas 
have  separated  and  are  ready  for 
pollination.  After  H.  Mtiller 


which  tends  to  secure  cross-pollination  is  highly  advantageous. 
One  of  the  most  effectual  means  of  preventing  self-pollination 
in  bisexual  flowers  is  the  maturing  of  the  stamens  at  a  different 
time  from  the  pistils,  known  as  dichogamy.  In  some  flowers,  as 
in  the  figwort  and  some  plantains  (Fig.  120),  the  pistils  mature 
first.  In  such  cases  the  pollen  from  older  flowers  (in  the  stami- 
nate  condition)  is  transferred  to  the  stigmas  of  recently  opened 
flowers  (in  the  pistillate  condition).  Pollination  of  the  plan- 
tain shown  in  Fig.  120  is  due  to  the  wind. 


132 


PRACTICAL  BOTANY 


Usually,  as  in  some  mallows  (Fig.  121)  and  in  Clerodendron 
(Fig.  122),  the  stamens  mature  first.  An  insect  visitor  to  a 
flower  in  the  staminate  condition  becomes  somewhat  covered 
with  pollen.  Then  flying  to  a  flower  in  the  pistillate  condition, 

he  is  sure  to  leave  pollen 
on  the  stigmas  and  thus  in- 
sure cross-pollination. 

It  is  common  to  find  the 
stamens  of  a  flower  matur- 
ing a  few  at  a  time,  as  in 
"  nasturtium,"  buckwheat 
(Fig.  114),  and  many  other 
flowers.  This  gives  more 
opportunities  for  insects  to 
carry  away  the  pollen  than 
would  be  possible  if  it  all 
matured  at  once. 

124.  Prevention  of  self- 
pollination:  dimorphism.  A 
means  of  preventing  self- 
pollination,  even  more  ef- 
fective than  is  dichogamy, 
is  found  in  the  structure 
of  flowers  in  which  some 
have  a  long  pistil  and  short  stamens,  others  a  short  pistil 
and  long  stamens.  This  condition  occurs  in  the  flowers  of 
bluets  (Fig.  123),  the  partridge  berry,  the  primrose,  and  some 
other  common  flowers.  It  is  easy  to  see  that  the  head  of  an 
insect  smeared  with  pollen  by  contact  with  the  anthers  of 
Fig.  123,  A,  would  just  come  into  contact  with  the  stigma 
of  B,  and  that  the  insect's  abdomen  covered  with  pollen  in 
B  would  just  touch  the  stigma  of  A.  All  the  flowers  on  an 
individual  plant  are  of  one  kind  (either  long-styled  or  short- 
styled),  and  the  pollen  is  of  two  sorts,  —  each  kind  sterile 
on  the  stigma  of  any  flower  of  similar  form  to  that  from 
which  it  came. 


FIG.  122.  Dichogamous  flower  of  Clero- 
dendron in  two  stages 

In  A  (the  earlier  stage)  the  stamens  are 
mature,  while  the  pistil  is  still  undevel- 
oped and  bent  to  one  side ;  in  B  (the  later 
stage)  the  stamens  have  withered  and 
the  stigmas  have  separated,  ready  for  the 
reception  of  pollen 


POLLINATION  AND  FERTILIZATION 


133 


125.  When  self-pollination  is  advantageous:  cleistogamous 
:flowers.  Some  flowers  are  usually  self-pollinated  unless  cross- 
pollinated  by  accident  or  by  human  agency.  Wheat  is  a 
:notable  instance  of  the  kind,  and  apparently  self-pollination 
•can  go  on  in  this  grain  for  a  long  period  without  injury  to  the 
fertility  or  the  robustness  of  the  offspring.1  Experiments  in 
raising  selected  varieties  of  tobacco  seem  to  show  that  in  this 
plant  self-fertilization,  for  several  generations  at  any  rate, 
produces  better  results  than  cross-fertilization.2 

Whenever  cross-pollination  by  the  wind  or  by  the  agency  of 
:animals  is  impossible,  it  is  evident  that  self-pollination  would 
be  advantageous,  since  it  is  infinitely  better  than  no  pollination 
;at  all.  Examples  of  the  impossibility  of  cross-pollination  are  the 
-cases  of  plants  which  grow  isolated  or  in  localities  in  which  the 
special  pollinating 

;animal  is  not  found,  a ' 

;as  American  yuc- 
cas in  European 
botanic  gardens. 
Many  highly  suc- 
cessful weeds  owe 
part  of  their  pre- 
dominance to  the 
fact  that  they  seed 
well  after  self- 
pollination. 

Since  occasional  cross-fertilization  appears  to  be  sufficient 
to  keep  up  the  strength  and  fertility  of  many  kinds  of  plants, 
it  would  seem  to  be  an  advantageous  plan  for  these  to  unite 
the  certainty  which  characterizes  self-pollination  with  the  re- 
newal of  strength  which  comes  from  cross-pollination.  Violets 
and  many  other  less  familiar  plants  unite  the  two  methods 

1  See  "Wheat :  Varieties,  Breeding,  Cultivation,"  Bulletin  62,  University 
of  Minn.  Agr.  Exp.  Sta.,  1899. 

2  See  "Tobacco  Breeding,"  Bulletin  96,  Bureau  of  Plant  Industry,  U,  S. 
Dept.  Agr.,  1907. 


FIG.  123.  Lengthwise  section  of  dimorphous  flower 
of  bluets 

A,  long-styled  form ;  J3,  short-styled  form ;  a,  anthers; 
s,  stigmas.  About  three  times  natural  size 


134  PEACTICAL  BOTANY 

by  producing  ordinary  showy  flowers  and  also  inconspicu- 
ous closed  or  cleistogamous  flowers.  The  latter  are,  in  violets, 
borne  on  flower  stalks  close  to  the  ground  (Fig.  124),  and 


FIG.  124.  A  violet,  with  cleistogamous  flowers 

The  objects  which  look  like  flower  buds  are  cleistogamous  flowers  in  various 

stages  of  development.    The  pods  are  the  fruit  of  similar  flowers  and  contain 

great  numbers  of  seeds.  The  plant  is  represented  as  it  appears  in  late  July  or 

earJy  August,  after  the  ordinary  flowers  have  disappeared 


POLLINATION  AND  FERTILIZATION  135 

usually  before  maturing  become  partially  buried  in  the  earth. 
The  cleistogamous  flowers  produce  many  more  seeds  than  the 
showy  ones,  but  the  latter  insure  occasional  cross-pollination.1 

1  On  the  general  subject  of  pollination  of  flowers  and  illustrations  of 
special  cases  see : 

Knuth-Davis,  Handbook  of  Flower  Pollination.  Clarendon  Press,  Oxford. 

Darwin,  The  Effects  of  Cross  and  Self  Fertilisation  in  the  Vegetable 
Kingdom.  D.  Appleton  and  Company,  New  York. 

Darwin,  Different  Forms  of  Flowers  on  Plants  of  the  Same  Species. 
D.  Appleton  and  Company,  New  York. 

Darwin,  The  Various  Contrivances  by  which  Orchids  are  fertilised  by 
Insects.  D.  Appleton  and  Company,  New  York.  ; 

Kerner-Oliver,  Natural  History  of  Plants,  Vol.  II.  Henry  Holt  and  Com- 
pany, New  York. 

Gray,  Structural  Botany.   American  Book  Company,  New  York.       | 

Weed,  Ten  New  England  Blossoms.  Houghton  Mifflin  Company,  Boston. 


CHAPTER  IX 


\--e 


SEEDS  AND  SEEDLINGS;  SEED  DISTRIBUTION 

126.  Gross  structure  of  seeds.  The  definition  of  the  term 
seed  has  already  been  given  (Sect.  22).  The  structure  of  seeds 
varies  so  greatly  in  details  that  in  this  place  it 
will  be  possible  to  describe  only  a  very  few 
typical  forms.1  The  most  important  parts  of 
ordinary  seeds  are : 

(1)  The  embryo,  or  miniature  plant. 

(2)  The  plant  food  stored  elsewhere  than 
in  the  embryo,  usually  known  as  endosperm? 

(3)  The  seed  coat  or  coats. 

All  of  these  parts  are  well  shown  in  Figs. 
125  and  126.    The  embryo  differs  greatly  in 
P  seeds   of   the  various 

groups  into  which  or- 
dinary seed  plants  are 
assembled  on  account 

FIG.  125.  Length-     of  tneir  relationship  to 

wise  section  of  each  other.  Many  em- 
bryos show  a  fairly 
well-defined  set  of  or- 
gans, —  the  hypocotyl, 
orli 
ledons,  or  seed  leaves ; 


]-hyp 


squash  seed 


hi,  hilum,  or  scar, 
marking  place  of 
attachment  to  the 
ovary ;  hyp,  hypo- 
cotyl ;  p,  plumule ; 
c,  cotyledon ;  e  (in- 
nermost layer  next 
to  cotyledon),  en- 


FIG.  126.  A  common  bean 

stem ;  the  coty-     split  ope£  ^  soakin" 

h,  hypocotyl,  lying  on  one  of 


dosperm  ;  t,  testa.      and     the     plumule,     or      the  cotyledons ;  g,  groove  in 
Two  and  one-half  n          '    *  the  other  cotyledon  where 


times  natural  size      seed  bud. 


the  hypocotyl  lay ;  p,  plumule 


1  See  also  Gray,  Structural  Botany,  chap.  viii.   American  Book  Company, 
New  York. 

2  When  this  reserve  food  is  formed  outside  of  the  embryo  sac  it  is  called 
perisperm. 

186 


SEEDS  AND  SEEDLINGS 


137 


C-- 


127.  Classification  according  to  number  of  cotyledons.    The 

seeds  of  one  great  division  of  seed  plants,  the  monocotyledons, 
—  comprising  grasses,  sedges,  palms,  lilies, 
and  many  other  groups,  —  have  one  cotyle- 
don (Fig.  127).  The  reserve  food  is,  as  is 
shown  in  that  figure,  mainly  stored  outside 
the  embryo. 

The   seeds  of  the   other  and   still  larger 
division,  the  dicotyledons,  have  two  cotyle- 
dons (Figs.  125  and  126).   The  plant  food  in 
the  seeds  of  dicotyledons  is  often  stored  in 
the  embryo  itself  (Fig.  126),  as  in  the  chest- 
nut, hazel,  beech, 
oak,  bean,  and  sun- 
flower;  or  often, 
like    that  of   the 
monocotyledon  ou  s 
onion(Fig.  127,^4), 
outside  of  the  em- 
bryo, as  in  buck- 
wheat, four-o'clock, 
castor  bean,  honey 
locust,  and  morn- 
ing-glory. 

128.  Forms  of 
reserve   material. 
The  study  of  the 
forms  of  the  food 
stored  in  seeds  is 
in      many     ways 
most     important. 
For  a  time,  usu- 
ally, the  seedling 
plant  depends  for 

its  growth  largely  on  the  reserves  in  the  seed  from  which  it 
springs.   And  the  most  concentrated  vegetable  food  used  by 


FIG.  127.   Seed  and  seedlings  of  onion 

A,  seed  ;  B-F,  successive  stages  in  development  of  the 

seedling ;  c,  cotyledon  ;  e,  endosperm  ;  /,  first  true  leaf ; 

7i,  hypocotyl ;  s,  slit  from  which /emerges;  r1?  primary 

root;  r2,  secondary  root.   A,  considerably  magnified 


138 


PRACTICAL  BOTANY 


man  and  other  animals  generally  consists  either  of  seeds  them- 
selves, as  in  the  case  of  the  grains,  nuts,  beans,  and  peas,  or 
of  manufactured  products,  such  as  oatmeal,  corn  meal,  flour, 
cornstarch,  cottonseed  oil,  derived  from  seeds. 

The  principal  plant  foods  found  in  the  seed  are  proteins 
of  many  kinds ;  carbohydrates  in  the  form  of  starch,  sugar,  or 
cellulose ;  and  fats  or  oils.  The  characteristics  of  these  vari- 
ous substances  can  be  learned  only  by  means  of  careful  labo- 
ratory work,  though  some  of  them  are  tolerably  familiar  to 
most  people.  Not  infrequently  the  different  kinds  of  reserve 
material  are  localized  in  special  parts  of  the 
seed.  In  the  grain  of  wheat  and  of  corn  the 
proteins  are  especially  abundant  in  the  trans- 
lucent flinty  outer  part  of  the  endosperm, 
while  the  starch  lies  mainly  in  the  interior 
white  portion  (Fig.  333).  The  oil  of  the  corn 
grain  is  stored  mainly  in  the  embryo,  so  that 
kinds  which  have  large  embryos  contain  a 
high  percentage  of  oil  and  those  with  small 
embryos  have  a  low  percentage  (Fig.  334). 

Every  seed  must  contain  some  protein 
material,  since  this  is  indispensable  to  the 
building  of  protoplasm,  and  no  growth  can 
take  place  without  it.  But  it  does  not  seem 
to  make  much  difference  whether  the  non-nitrogenous  food  in 
the  seed  consists  mainly  of  starch  as  in  rice,  of  oil  as  in  Brazil 
nuts,  or  of  cellulose  as  in  coffee  and  date  seeds.  Along  with 
much  starch,  many  of  the  grains,  particularly  millet,  contain 
a  good  deal  of  gum,  sugar,  and  fat.  The  fact  that  sugar  is  not 
usually  abundant  in  seeds  may  be  due  to  the  readiness  with 
which  it  dissolves  in  water,  which  might  lead  to  some  of  it 
becoming  lost  in  the  soil  during  germination. 

129.  The  seed  coat.  The  seed  coat  protects  the  embryo  (and 
the  endosperm,  when  present)  from  mechanical  injuries.  In 
order  to  allow  germination  to  begin,  either  the  general  surface 
of  the  coat  must,  as  in  most  seeds,  be  porous  enough  to  absorb 


FIG.  128.  Diagram 
of  lengthwise  sec- 
tion of  a  grain  of 
wheat 

en,  endosperm ;  em, 

embryo.  Somewhat 

magnified 


SEEDS  AND  SEEDLINGS 


139 


sc 


v.c-- 


moisture,  or,  in  such  hard-shelled  seeds  as  the  coconut,  hick- 
ory nuts,  walnuts,  and  butternuts,  there  must  be  a  thin  or 
soft-walled  place  through  which  water  can  enter.  Usually  the 
little  opening  in  the  ovule, 
known  as  the  micropyle  (Fig. 
109,  w),  remains  in  the  seed 
and  serves  to  admit  moisture. 

The  coats  of  many  seeds 
have  wings  or  outgrowths  of 
hairs  which  aid  in  their  dis- 
persal, as  already  mentioned. 
Other  modifications  in  the 
coats  of  seeds  apparently,  in 
some  cases,  serve  as  aids  in 
their  dispersal,  and  others  as 
means  of  preventing  the  seed 
from  being  eaten  by  animals. 

130.  Conditions  for  germi- 
nation. A  sound,  live  seed  will 
germinate  or  sprout  when  suit- 
able conditions  are  present. 
The  requisites  for  germina- 
tion are : 


per 


r.c~- 


f 


(1)  The   proper   tempera- 
ture. 

(2)  Enough  moisture. 

(3)  Air  or  oxygen.1 

The  temperature  most  fa- 


FIG.  129.  Lengthwise  section  (some- 
what diagrammatic)  through  the  em- 
bryo end  of  a  grain  of  wheat 

en,  endosperm ;  sc,  scutellum,  or  absorb- 
ing portion  of  cotyledon;  c.t,  cellular 
tissue  (containing  much  oil)  in  which  the 
cotyledon  is  embedded ;  v.c,  vegetative 
cone  or  growing  point;  h,  hypocotyl; 
r.c,  rootcap ;  per,  periderm,  or  coating 
of  grain ;  /,  scar  to  which  the  f  uniculus  or 
seed  stalk  was  attached.  After  Warming. 
Magnified  about  26  diameters 


vorable  for  germination  varies 
with  the  kind  of  seed ;  for  any  given  kind  there  seems  to  be 
a  lowest  limit,  a  most  favorable  (optimum)  temperature,  and  a 
highest  limit.  The  approximate  temperatures  for  a  few  species 
are  given  on  the  next  page  (in  Fahrenheit  degrees).2 

1  Some  seeds  begin  to  germinate  without  air,  but  soon  die  unless  it  is 
supplied  to  them. 

2  See  Detmer,  Keimungsprocess  der  Samen,  chap.  iii.    G.  Fischer,  Jena. 


140 


PEACTICAL  BOTANY 
GERMINATION  TEMPERATURES 


LOWEST 

HIGHEST 

MOST  FAVORABLK 

Barley  

32°-41° 

100  4° 

84° 

Wheat                       . 

32°-41° 

107  6° 

84° 

Scarlet  runner    .     .     .  '  > 

49° 

115° 

91.4° 

Indian  corn    

49° 

115° 

91.4° 

Squash  •     <k 

57° 

115° 

91  4° 

Muskmelon  and  cucumber 

60° 

117° 

93° 

Most  farmers  have  learned  by  experience  that  the  tempera- 
ture requirements  of  all  kinds  of  seeds  are  not  the  same.  All 
know,  for  example,  that  if  corn  is  planted  before  the  ground  is 
warm  enough,  it  will  decay  and  have  to  be  replanted,  but  that 
peas  can  be  sown  very  soon  after  the  frost  is  out  of  the  ground. 

There  is  moisture  enough  in  a  few  kinds  of  seeds,  like  those 
of  the  willow  and  the  poplar,  to  allow  them  to  begin  to  germi- 
nate as  soon  as  they  are  ripe.  But  most  seeds  need  to  be  sup- 
plied with  moisture  from  without.  Too  little  moisture  causes 
them  to  germinate  very  slowly,  as  is  often  noticed  during 
spring  droughts,  while  immersing  them  in  water  causes  many 
kinds  to  rot  because  the  air  supply  is  not  sufficient. 

Lack  of  air  as  a  hindrance  to  germination  is  particularly 
likely  to  occur  when  seeds  are  planted  too  deep  in  clay  soils. 
In  warm,  open  soils  there  is  usually  air  enough,  and  the  dan- 
ger encountered  is  that  of  drying  up,  from  shallow  planting. 

131.  Preparation  of  seeds  for  germination.  A  few  kinds  of 
seeds,  as  above  mentioned,  may  sprout  as  soon  as  they  are  ripe. 
Most  sorts,  however,  need  a  period  of  rest  and  comparative 
dryness  before  they  will  grow.  The  importance  of  drying 
seeds  is  well  shown  in  the  case  of  corn.  Kiln-dried  corn  has, 
in  one  instance,  been  shown  to  yield  1C  bushels  per  acre  more 
than  air-dried  seed  of  the  same  variety. 


SEEDS  AND  SEEDLINGS 


141 


After  the  rest  period  the  time  required  for  germination 
varies  greatly.1  Grains,  grasses,  and  many  seeds  of  herbs  of 
the  Pea  family  germinate  in  2  to  8  days,  most  seeds  of  plants 
of  the  Parsley  family  in  about  14  days.  Seeds  of  trees  and 
shrubs  usually  require  much  more  time  ;  for  example,  those  of 
the  hornbeam  and  ash  are  said 
not  to  grow  until  the  second 
spring  after  they  are  planted. 


FIG.  130.  Wheat  seedling 

g,  the  grain ;  GL,  ground  line ; 

s.l,  sheathing  leaf ;  I,  first  true 

leaf.   One  half  natural  size 


FIG.  131.  Corn  seedling 

g,  the  grain ;  GL,  ground  line ;  r,  first 

root,  from  the  tip  of  the  embryo ;  r', 

later  roots;  s.l,  sheathing  leaf.   One 

half  natural  size 


132.  Types  of  seedlings.  Seedlings2  may  be  divided  into  two 
groups,  monocotyledonous  seedlings  and  dicotyledonous  seedlings. 
Those  of  the  dicotyledonous  group  may  be  further  sub-divided 
into  plants  with  underground  cotyledons,  as  the  pea  and  the  oak, 

1  See  Crocker,  "R61e  of  Seed  Coats  in  Delayed  Germination,"  Botanical 
Gazette  42,  October,  1906. 

2  Not  considering  those  of  coniferous  shrubs  and  trees  (Fig.  266). 


142 


PRACTICAL  BOTANY 


and  those  with   aboveground  cotyledons,   as  the  maple,  bean, 
squash,  and  morning-glory. 

The  monocotyledonous  seedling  may  or  may  not  raise  its 
single  cotyledon  out  of  the  ground  after  germination.  The 
onion  does  so  (Fig.  127)  but  the  grains  do  not  (Figs.  130,  131). 
In  all  the  larger  grains  (as  in  corn)  the  fitness  of  the  plumule 
for  piercing  hard  clods  or  bits  of  sod  is  very  noticeable,  and 
serves  the  plant  well  in  breaking  out  of 
the  ground  against  opposition. 

Dicotyledonous  seedlings  with  under- 
ground cotyledons,  like  the  pea  (Fig. 
132),  are  better  able  to  force  their  way 
out  of  the  ground  if  planted  deep  than 
are  most  of  those  with  aboveground  coty- 
ledons, like  the  bean  (Fig.  133).  There- 
fore even  large  seeds  of  the  latter  type, 
like  those  of  the  bean,  melon,  cucumber, 
and  squash,  should  not  be  planted  deep. 
Very  minute  seeds,  like  those  of  portu- 
laca,  poppy,  and  most  plants  of  the  Pink 
family,  should  be  planted  on  the  surface 
of  well-raked  fine  earth  and  then  barely 
covered  by  sifting  over  them  a  little  of 
the  finest  loam,  or  by  dragging  a  trowel 
or  other  suitable  implement  lightly  back 
and  forth  over  the  bed. 
133.  Function  of  the  cotyledons.  In  many  seeds  of  mono- 
cotyledons, as  the  grains,  the  cotyledon  does  not  emerge  from 
the  seed  nor  rise  above  the  surface  of  the  ground.  It  forms  an 
absorbing  organ  known  as  the  scutellum  (Fig.  129,  so),  which 
serves  to  take  up  liquefied  plant  food  from  the  endosperm  and 
transfer  it  to  the  growing  embryo.  In  the  seed  of  the  date 
palm  it  acts  much  in  the  same  way.  Other  monocotyledonous 
plants,  like  the  onion,  bring  the  cotyledon  out  of  the  ground 
(often  with  the  seed  coat  attached)  and  then  proceed  to  de- 
velop ordinary  foliage  leaves  (Fig.  127). 


FIG.  132.  Pea  seedling 

cot,  the  unopened  cotyle- 
dons ;  GL,  ground  line ;  r, 
root ;  «,  stem ;  I,  rudimen- 
tary leaves.  One  half  nat- 
ural size 


SEEDS  AND  SEEDLINGS 


143 


In  dicotyledonous  seeds  of  the  type  of  the  pea,  the  horse- 
chestnut,  and  the  buckeye,  the  cotyledons  remain  inclosed  in 
the  seed  coat  and  underground 
(Fig.  132),  where  they  become 
emptied  of  their  contents.  They 
are  so  loaded  with  reserve  ma- 
terial that  they  could  not  serve 
any  useful  purpose  if  they  were 
to  emerge  into  the  air  and  light. 

In  the  bean,  they 
are  raised  into  the  air, 
turn  green,  develop 
stomata,  and  probably 
for  a  short  time  do 
some  photosynthetic 
work,  but  soon  wither 
and  fall  off. 

In  the  squash,  pump- 
kin, and  most  dicoty- 
ledonous plants  of  the 
farm  and  garden,  the 
cotyledons  become  for 
a  considerable  time 
active  green  leaves, 
but  they  are  shorter- 
lived  than  the  sub- 
sequent leaves  of  the 
plant,  are  opposite  or 
nearly  so  (while  the 
later  leaves  may  be 
opposite  or  alternate), 
are  usually  smaller 
than  other  leaves,  and 
their  shape  always 
differs  from  that  of  the  permanent  leaves  of  the  plant.  Even 
in  those  cases  where  the  cotyledon  for  a  time  becomes  wholly 


FIG.  133.  Two  stages  in  the  growth  of  the  bean 
seedling 

In  the  younger  stage  the  arch  of  the  hypocotyl  is 
but  little  above  the  surface ;  in  the  older  stage  the 
cotyledons  have  separated,  the  first  internode  has 
elongated  considerably,  and  the  first  pair  of  foli- 
age leaves  has  expanded.  Cot,  cotyledon;  h,  hy- 
pocotyl ;  ha,  hypocotyl  arch ;  i,  internode ;  I,  leaf ; 
n,  taproot  which  proceeded  from  the  tip  of  the 
hypocotyl;  r2,  branches  of  n.  Natural  size 


144 


PRACTICAL  BOTANY 


leaf -like  in  its  appearance,  as  in  buckwheat  and  the  castor  bean, 
its  activity  differs  from  that  of  the  permanent  leaves.  The  rate 
of  transpiration  for  equal  areas  of  such  cotyledons,  when  com- 
pared with  that  of  the  later  leaves, 
has  been  found  to  be  from  one 
and  a  half  to  two  times  as  great. 
It  is  easy  to  see  that  in  a 
general  way  the  readiness  with 
which  some  cotyledons  assume 
the  character  of  temporary  foliage 
leaves  depends  on  their  com- 
parative freedom  from  deposits 
of  plant  food.  For  this  reason 
some  of  the  most  leaf-like  coty- 
ledons, like  those  of  the  buck- 
wheat and  the  morning-glory,  are 
found  in  seeds  with  abundant 
endosperm. 

134.  Action  of  enzymes  on  re- 
serve material  of  seeds.  One  of 
the  most  surprising  things  about 
the  early  growth  of  seedlings 
is  the  rapid  way  in  which  many 
kinds  begin  to  grow  even  in  saw- 
dust or  on  moist  blotting  paper. 
Evidently  the  plant  food  at  the 
start  must  all  come  from  the 
seed,  and  the  removal  of  most 
of  the  reserve  food  of  the  seed 
greatly  retards  the  growth  of  the 
seedling  (Fig.  134).  It  is  not 
at  once  clear  how  the  proteins 

and  the  starch  of  some  seeds  and  the  oil  or  cellulose  of  others 
are  so  quickly  withdrawn  from  them  and  transferred  to  the 
growing  plantlet.  Most  of  the  reserve  substances  found  in 
seeds  are  soluble  with  difficulty  or  quite  insoluble  in  water 


FIG.  134.   Pea  seedlings  growing 
in  water 

A,  deprived  of  both  cotyledons;  /?, 
with  cotyledons  uninjured 


SEEDS  AND  SEEDLINGS  145 

or  the  watery  sap  of  plants.  But  the  insoluble  substances  be- 
fore being  transferred  into  the  seedling  are  transformed  into 
soluble  ones.  This  is  due  to  the  action  of  certain  substances 
known  as  enzymes  or  soluble  ferments.  An  enzyme  as  found  in 
seeds  is  a  substance  secreted  by  the  plant  for  the  purpose  of 
digesting  or  rendering  soluble  such  plant  foods  as  require 
digestive  action  before  they  can  be  absorbed  by  the  tissues 
of  the  young  seedling.  Much  has  yet  to  be  learned  about  the 
nature,  occurrence,  and  action  of  the  enzymes.  In  most  seeds 
enzymes  occur  inside  the  cells  along  with  the  reserve  mate- 
rials, and  so  at  suitable  temperatures,  in  presence  of  moisture, 
the  digestion  of  the  cell  contents  can  take  place  everywhere 
throughout  the  seed.  The  scutellum  of  the  grains  (Fig.  1 29,  sc) 
secretes,  from  its  outer  layer,  which  is  in  contact  with  the 
endosperm,  two  kinds  of  enzymes,  and  rapidly  digests  the  sur- 
rounding endosperm. 

At  very  low  temperatures,  enzymes  cannot  carry  on  their 
work.  Each  kind  has  a  special  temperature  at  which  it  is 
most  active ;  for  many  kinds  this  ranges  between  86°  and 
113°  Fahrenheit  (30°  to  45°  Centigrade).  Evidently  the  low- 
est temperature  at  which  the  enzyme  of  a  given  seed  can  act 
must  limit  the  temperature  at  which  germination  can  go  on  l ; 
and  the  temperature  at  which  the  growth  of  the  very  young 
seedling  is  most  rapid  must  be  not  far  from  the  temperature 
at  which  the  enzyme  of  its  seed  is  most  effective.  * 

Of  the  many  kinds  of  enzymes  known,  two  of  the  classes  most 
important  in  plant  physiology  are  those  known  as  diastases, 
which  change  starch  into  sugar,  and  those  known  as  trypsins, 
which  render  insoluble  proteins  soluble.  The  most  familiar 
case  of  action  of  enzymes  on  a  large  scale  is  the  malting  of 
barley,  in  which  the  starch  of  the  grain  is  converted  into  a 
sugar  by  diastase.  It  is  said  that  diastase  can  change  10,000 
times  its  own  bulk  of  starch  into  sugar.2 

1  See  the  table  of  germination  temperatures,  Sect.  130. 

2  On  digestion  and  enzymes  consult  J.  R.  Green,  Vegetable  Physiology, 
chap.  xvi.   P.  Blakiston's  Son  and  Co.,  Philadelphia. 


146 


PEACTICAL  BOTANY 
SEED  DISTRIBUTION 


135.  Usefulness  of  the  seed.  People  in  general,  no  matter 
how  familiar  they  may  be  with  seeds,  do  not  stop  to  consider 
what  the  seed  means  in  the  perpetuation  of  any  species  of 


FIG,  135.  Fruits  of  Spanish  needles  (Bidens) 
Natural  size  and  twice  natural  size 

plant.  Some  seed  plants,  it  is  true,  manage  to  perpetuate 
themselves  for  an  indefinite  tune  by  vegetative  methods,  as 
by  root  buds,  by  various  kinds  of  stem  propagation,  or  even 


SEED  DISTRIBUTION 


147 


by  their  leaves.  But  even  perennials  generally  depend  upon 
the  growth  of  seeds  to  continue  the  species.  A  forest  of  white 
pines,  for  example,  when  all  its  trees  have  died  of  old  age  or 
been  killed  by  plant  or  insect  enemies,  by  destructive  winds 
or  forest  fires,  can  only  be  renewed  by  the  growth  of  young 
pines  from  the  seed.  And  in  the  case  of  annual  plants  all  the 


FIG.  136.  Dandelion  fruits 

a,  akene ;  6,  beak  of  pappus;  br,  bracts;  p,  pappus  (representing  the  limb  of  the 
calyx) ;  r,  common  receptacle  for  all  the  fruits.   Twice  natural  size 

individuals  in  existence  at  any  one  time  will  have  died  in  a 
year,  or  little  more,  from  that  date,  to  be  replaced  by  a  new 
crop  sprung  from  seeds. 

It  is  important  to  notice  how  well  suited  most  seeds  are  to 
withstand  conditions  that  would  kill  ordinary  plants.  Seeds 
are  not  injured  by  the  lowest  natural  temperatures,  and  they 
resist  considerably  higher  temperatures  than  those  found  in 
most  climates.  Lack  of  moisture  does  not  usually  harm  them. 
And  while  some  kinds  of  seeds  remain  capable  of  sprouting 
only  for  a  few  days,  most  kinds  will  remain  good  for  a  year 
and  many  for  several  years.  The  seed  is  a  matured  ovule 


148  PRACTICAL  BOTANY 

containing  a  new  plant.  Defined  from  its  function,  it  is  a  highly 
portable  and  not  easily  injured  package,  in  which  the  rudi- 
ments of  a  plant,  like  its  parent,  may  be  carried  about  and  hold 
life  over  from  season  to  season. 

136.  Need  of  seed  distribution.  The  successive  crops  of  farm 
and  garden  annuals  are  secured  by  careful  seed  planting  in 
prepared  soil.    The  seeds  of  wild  plants  are  also  sown,  on  a 
still  more  extensive  scale,  by  natural  agencies.  In  any  country 
the  relative  numbers  of  most  kinds  of  wild  seed  plants  usually 
remain  from  year  to  year  without  great  changes  except  those 
which  are  brought  about  by  human  interference.    This  fact  is 
evidence  enough  that  seeds  in  unimaginable  numbers  must 
be  scattered  about  in  such  a  way  as  to  make  good  the  losses 
in  the  plant  population  of  the  world  due  to  all  destructive 
causes.    The  means  of  seed  distribution  will  be  taken  up  in 
Sects.  140  and  141. 

137.  The  struggle  for  existence.  Only  a  small  proportion  of 
all  the  seeds  annually  produced  can  have  a  chance  to  grow. 
The  resulting  contest  among  plants  for  a  foothold  and  for 
the  means  of  subsistence  forms  one  portion  of  what  the  great 
English  naturalist,  Charles  Darwin,  called  the  struggle  for  exist- 
ence.   It  is  shown  by  careful  calculation  that  about  .5,300,000 
acres  of  land  could  be  sown  with  the  wheat  grown  at  the  end 
of  fifteen  years  from  a  single  parent  kernel,  if  every  grain 
were  to  grow  and  live.  But  the  wheat  plant  does  not  produce 
a  very  large  number  of  seeds.    The  so-called  Russian  thistle 
(Salsola  Kali,  var.  tenuifolia),  a  most  troublesome  weed,  bears 
from  20,000  to  200,000  seeds.  Taking  the  moderate  estimate 
of  25,000  seeds  to  a  plant,  their  offspring  (if  all  the  seeds  grew) 
would  number  625,000,000  individuals,  and  the  next  genera- 
tion would  number  15,625,000,000,000.  Supposing  each  plant 
to  have  a  diameter  of  about  three  feet  and  to  occupy  an  area 
of  seven  square  feet,  the  student  can  readily  calculate  how 
many  square   miles  of  territory  the  number  of  plants  last 
named  would  cover,  if  actually  in  contact  with  each  other 
throughout  their  circumferences. 


SEED  DISTRIBUTION  149 

The  fact  that  any  species,  such  as  the  ordinary  ragweed 
(Ambrosia  artemisicefolia),  common  throughout  most  of  the 
United  States,  does  not  promptly  overrun  all  those  portions 
of  the  earth's  surface  suited  to  its  growth  is  due  to : 

(1)  Lack  of  sufficiently  thorough  and  rapid  means  of  seed 
distribution. 

(2)  Multiplication  of  insect  and  plant  enemies  of  the  species 
(often  not  important). 

(3)  Overcrowding  or  competition  between  individuals  of 
the  same  species  (other  ragweeds)  or  of  other  species. 

138.  How  competition  kills.  The  result  of  competition 
among  plants  is  sometimes  to  make  the  overcrowded  individ- 
uals dwarfish  and  unfruitful,  or  at  other  times  to  kill  them 
outright.  The  means  by  which  the  successful  individuals 
weaken  or  kill  their  neighbors  are  mainly: 

(1)  Overshadowing,  resulting  in  deficient  photosynthesis 
in  the  shaded  plants  from  lack  of  light. 

(2)  Robbing  the  defeated  plants  of  water. 

(3)  Robbing  them  of  soluble  salts  (nitrates,  phosphates,  and 
so  on,  from  the  soil). 

The  deprivation  of  sufficient  water  and  salts  interferes 
with  the  nutrition  of  the  overcrowded  plants  and  may  soon 
completely  stop  their  growth. 

The  extent  and  reality  of  the  competition  here  merely  out- 
lined can  be  understood  only  by  aid  of  careful  field  work. 
Weedy  ground  may  be  found  which  contains  as  many  as  a 
thousand  seedlings  to  the  square  foot,  and  if  a  small  area  of 
such  ground  is  isolated  and  watched,  the  struggle  for  exist- 
ence may  be  followed  to  its  end,  with  only  one  or  two  of  the 
thousand  surviving.1  It  must  be  remembered  that  multitudes 
of  seeds  get  no  start  in  life  as  seedlings,  and  so  do  not  even 
enter  into  competition,  either  from  failure  to  lodge  in  a  place 

1  See  also  Charles  Darwin,  Origin  of  Species,  chap,  iii  (D.  Appleton  and 
Company,  New  York),  L.  H.  Bailey,  Survival  of  the  Unlike,  pp.  258-261 
(The  Macmillan  Company,  New  York),  and  Bergen  and  Davis,  Principles 
of  Botany,  pp.  448-450  (Ginn  and  Company,  Boston). 


FIG.  137.  Winged  fruits 
of  maple 

One  half  natural  size 


FIG.  138.  Winged  fruits  of 
Ailardhus 

One  half  natural  size 


FIG.  139.  Winged  fruits  of 
red  elm 

Natural  size 


150 


SEED  DISTRIBUTION 


151 


in  which  they  may  germinate,  or  because  they  are  promptly 
destroyed  by  birds  or  other  animals,  or  by  molds  or  other 
organisms  which  cause  them  to  decay. 

139.  Fruits.  The  term  fruit  in  its  most  limited  botanical 
sense  means  the  ripened  ovary  with  its  seeds  and  other  con- 
tents. In  a  grape  there  is  nothing  more  than  this.  In  a  currant 


FIG.  140.  Bract-winged  fruits  of  linden 

/,  fruits  of  linden,  with  a  wing-like  bract  (6)  by  means  of  which  they  are  blown 
about  by  the  wind.  One  half  natural  size 

or  gooseberry,  however,  the  thickened  and  fleshy  calyx  sur- 
rounds the  fruit  proper  and  forms  a  part  of  what  is  usually 
called  the  fruit  by  botanists.  In  many  dry  fruits,  such  as  those 
of  Spanish  needles  (Bidens,  Fig.  135)  and  of  the  dandelion 
(Fig.  136),  the  limb  of  the  calyx  forms  some  sort  of  hook, 
spine,  plume,  or  other  appendage,  and  the  whole  is  usually 
spoken  of  as  the  fruit.  Not  infrequently  the  receptacle  is 


152 


PRACTICAL  BOTANY 


enlarged  and  united  to  the  ripened  ovary,  and  is  counted  part 
of  the  fruit,  or  many  ovaries  may  be  joined  by  the  receptacle 
into  a  single  mass,  as  in  the  strawberry. 


FIG.  141.  Fruits  of  ironweed  in  heads,  and  some  separate  fruits 
The  latter  one  and  one-half  times  natural  size 

140.  Mechanisms  which  aid  in  the  distribution  of  seeds. 
Seeds  and  fruits  are  in  many  instances  so  constructed  that 
they  are  very  likely  to  be  carried  about  by  wind,  water,  or 
animals.  The  winged  seeds  of  the  catalpa  and  the  tufted  ones 
of  the  willow  are  readily  carried  long  distances  by  the  wind. 
So,  too,  are  the  winged  fruits  of  the  maple,  the  Ailanthus,  and 


SEED  DISTRIBUTION 


153 


the  elm  (Figs.  137-139),  and  the  tufted  ones  of  the  thistle 
and  the  ironweed  (Fig.  141).  The  seed  capsules  of  the  poppy, 
the  morning-glory  (Fig.  142),  the  evening  primrose  (Fig.  144), 


FIG.  142.    Seed  pods  of  morning- 
glory  beginning  to  open,  so  as  to 
allow  the  seeds  to  rattle  out,  a  few 
at  a  time 

One  half  natural  size 


FIG.  143.  Two  capsules  of  the  wild 

balsam  and  a  third  detached,  split 

open,  and  curled  up  as  it  appears 

after  throwing  the  seeds  about 

Two  thirds  natural  size 


FIG.  144.  Pods  of  evening  prim- 
rose open  at  the  top  and  allow- 
ing the  seeds  to  escape  gradually 

Three  fourths  natural  size 


FIG.  145.    Fruit  of  crane's-bill, 
the  carpels  splitting  away  from 
a  central  column  and  thus  throw- 
ing the  seeds  about 

Reduced 


154 


PRACTICAL  BOTANY 


the  larkspur,  and  many  other  plants,  open  at  or  near  the  top, 
and  for  weeks  allow  the  seeds  to  be  scattered  by  the  wind  when- 
ever the  stalks  of  the  cap- 
sules are  swayed  back  and 
forth  by  it.  Such  stalks  are 
still  more  strongly  swayed 
by  a  passing  animal,  and 


FIG.  146.  Burs  of  sticktights  (Desmodium) 
One  half  natural  size 

then  throw  many  seeds  directly 
at  the  animal,  into  whose  fur 
they  fall  and  are  carried  till 
they  shake  out. 

Some  fruits  or  clusters  of 
them,  as  white  pine  cones,  or 
whole  plants,  known  as  tum- 
bleweeds  (Fig.  356),  are  rolled 

along  the  ground  by  the  wind,  carrying  with  them  multitudes  of 
seeds.  Among  the  commonest  are  old  witch  grass  {Panicum), 
tumbleweed  (Amaranthus),  and  the  "  Russian  thistle  "  (Sahola). 


FIG.  147.   Head  of  fruits  of  avens 

and  some  of  the  separate,  bur-like 

fruits,  with  hook-like  remains  of 

the  style 

The  latter  one  and  one-half  times 
natural  size 


SEED  DISTRIBUTION 


155 


Water  plants  very  commonly  produce  seeds  or  fruits  which 
will  float,  and  these  are  often  carried  for  miles  by  the  water,  to 
lodge  and  grow  long  after  their  voyage  began.  It  is  supposed 
that  many  uninhabited  islands  of  the  South  Seas  have  in  this 
way  been  planted  with  coco  palms. 

Various  devices  throw  seeds  about  (Figs.  143  and  145),  espe- 
cially when  disturbed  by  an  animal,  into  whose  fur  the  seeds 
may  fall.  Burs  in 
great  numbers  are 
carried  about  by 
animals,  sometimes 
clinging  for  months 
to  the  hair,  fur,  or 
feathers  (Figs.  146 
and  147). 

141.  Dispersal  of 
edible  seeds.  Edible 
seeds  and  fruits  — 
such  as  nuts,  the 
grains,  berries,  and 
stone  fruits  like  FIG.  148.  Fruit  of  the  wild  black  cherry,  a  valu- 
plums  and  cherries  able  timber  tree 

—  are  often  carried 
long  distances  by 
animals.  They  are  frequently  swallowed,  and  later  voided  un- 
digested and  in  a  condition  to  grow.  In  this  way  wild  cherries 
(Fig.  148)  and  wild  apples  are  planted  about  pastures  and  in 
open  woods.  So,  too,  raspberry,  currant,  and -gooseberry  bushes, 
asparagus,  and  bittersweet  may  be  found  growing  in  the  forks 
of  trees  high  above  the  ground.  Squirrels,  blue  jays,  and  some 
other  animals  carry  away  nuts  and  bury  them,  often  leaving 
them  to  grow  the  following  spring  (Fig.  325). 1 

1  On  the  general  subject  of  seed  dispersal  see  Kerner-Oliver,  Natural 
History  of  Plants,  pp.  833-877  (Henry  Holt  and  Company,  New  York)  ;  also 
Beal,  Seed  Dispersal  (Ginn  and  Company,  Boston). 


The  seeds,  which  are  hard  and  indigestible,  are  dis- 
seminated mainly  by  birds.    One  half  natural  size 


CHAPTER  X 
THE  GREAT  GROUPS  OF  PLANTS 

142.  The  basis  of  classification.  In  the  preceding  chapters 
little    has  been   said  about   classifying   plants  into  groups. 
Practically  all  the  plants  discussed  so  far  belong   to    one 
group,  and  since  flowers  and  seeds  are  characteristic  structures 
in  these  plants,  the  group  is  usually  spoken  of  as  the  Flower- 
ing or  Seed  Plants.     Throughout  the  entire  plant  kingdom 
one  or  more  kinds  of  structures  are  generally  used  as  the 
basis  for  arranging  plants  into  groups.    What  a  plant  may  do 
with  these  different  structures,  or  where  the  plant  lives,  may 
have  some  influence  upon  the  classification  of  the  plant,  but 
ordinarily  these  things  all  give  way  to  considerations  of  struc- 
ture in  determining  the  group  to  which  a  plant  belongs. 

It  is  true  that  such  expressions  as  "  desert  plants,"  or 
"parasitic  plants,"  are  used  to  group  together  plants  that  live 
in  certain  kinds  of  regions,  or  that  live  by  means  of  certain 
processes,  and  such  bases  of  classification  are  most  interest- 
ing and  profitable ;  but  it  has  been  found  much  more  con- 
venient and  more  satisfactory  to  arrange  the  great  groups 
upon  the  basis  of  structure  and  form.  Beginners  in  botany 
are  often  more  interested  in  what  plants  are  doing  than  in 
what  their  structures  are,  but  we  must  know  what  the  struc- 
tures are  in  order  to  understand  what  is  being  done.  Also 
a  better  degree  of  uniformity  in  classification  is  obtained  by 
using  plant  structures  as  its  basis. 

143.  The  meaning  of*  genus  and  species.    In  most  wooded 
regions  one  or  more  kinds  of  oaks  may  be  found.   The  follow- 
ing kinds  are  common,  and  are  known  to  many  people  who 
have  not  studied  botany :  white  oak,  bur  oak,  red  oak,  black 
oak,  blackjack  oak,  live  oak,  and  several  other  kinds.    While 

156 


FIG.  149.  A  group  of  leaves  and  acorns  illustrating  some  of  the  differences 
.    between  six  species  of  oak  (Quercus) 

A,  the  white  oak  (Q.  alba) ;  B,  the  red  oak  (Q.  rubra)  •  C,  the  bur  oak  (Q.  macro- 

carpa) ;  D,  the  black  oak  (Q.  velutina) ;  E,  the  blackjack  oak  (Q.  marylandica) ; 

F,  the  live  oak  (Q.  virginiana).   The  acorns  are  about  three  fourths  natural  size 

and  the  leaves  less  than  one  half  natural  size.    Modified  from  R.  B.  Hough 

157 


158  PRACTICAL  BOTANY 

all  these  are  oaks,  and  bear  to  one  another  many  resemblances 
in  form  of  tree,  form  of  leaf,  and  in  the  proportion  of  parts, 
there  are  sufficient  differences  in  form  to  distinguish  them 
one  from  another.  The  botanist  uses  a  genus  name,  which  is 
Quercus,  to  include  all  the  oaks,  and  to  this  genus  name  he 
adds  a  species  (specific)  name  by  which  to  indicate  the  par- 
ticular kind  of  oak  of  which  he  is  speaking.  In  names  of 
many  plants  the  specific  name  suggests  a  prominent  character- 
istic of  the  particular  kind  of  plant  to  which  the  name  refers ; 
as  in  Quercus  alba,  alba,  meaning  "white,"  refers  to  the  whitish 
bark  of  the  tree;  and  in  Quercus  nigra,  nigra  refers  to  the 
blackish  bark.  A  list  of  six  of  the  oaks,  together  with  the 
leaf  outlines  and  drawings  of  the  acorns  (Fig.  149),  should 
help  to  make  more  clear  the  meaning  of  genus  and  species. 
This  meaning  needs  to  be  understood,  since  we  usually  speak 
of  plants  by  their  common  names  or  by  their  generic  names, 
and  often  it  is  necessary  also  to  use  the  specific  names. 

144.  The  leading  groups  of  plants.  Quite  similar  plants  are 
grouped  together  into  one  species,  and  species  that  closely  re- 
semble one  another  are  grouped  together  into  one  genus.  In 
the  same  way  similar  genera  (plural  of  genus')  are  grouped 
together  into  one  family,  and  families  of  close  resemblances 
are  grouped  into  an  order.  Orders  are  grouped  into  sub-classes 
or  directly  into  classes,  and  the  classes  into  great  groups,  of 
which  there  are  four.  These  four  great  groups  together  con- 
stitute the  plant  kingdom.  Other  intermediate  groups  are 
sometimes  used. 

Of  the  four  great  groups  of  plants,  the  one  which  includes 
the  flowering,  or  seed  plants,  is  the  spermatophytes,  a  name 
which  means  "  seed  plants."  The  spermatophytes  are  divided 
into  the  angiosperms,  or  plants  with  inclosed  seeds,  and  the 
gymnosperms,  or  plants  with  exposed  seeds.  The  group  next 
below  the  spermatophytes  is  the  pteridophytes,  or  fern  plants, 
the  group  which  includes  the  true  ferns  and  certain  other 
plants  which  are  rather  rare.  Next  below  the  pteridophytes 
is  the  bryophytes,  or  moss  plants,  consisting  of  the  mosses  and 


THE  GREAT  GROUPS  OF  PLANTS      159 

liverworts.  The  lowest  group  is  the  thallophytes,  the  lowly  or 
prostrate  plants,  which  group  includes  the  fission  plants,  the 
fungi  and  the  algce.  It  is  the  last-named  group,  the  thallo- 
phytes, which  we  shall  first  consider. 

145.  Some  aspects  under  which  plants  are  studied.    The 
study  of  the  great  groups,  their  subdivisions,  and  the  proper 
classification  of  plants,  is  known  as  taxonomy,  or  systematic 
botany.   The  study  of  plant  structures,  their  similarities,  differ- 
ences, and  relationships  is  known  as  morphology.   Special  study 
of  the  cell  is  cytology.    Plant  activities  or  work  and  their  rela- 
tions to  the  immediate  surroundings  of  the  plant  are  included 
in  physiology,  while  the  relationships  of  plants  to  one  another 
and  to  the  environment  in  general  is  ecology.    One  phase  of 
ecology  deals  with  the  distribution  of  plants  over  the  earth 
and  is  known  as  ecological  plant  geography.     The  study  of 
plant  diseases  is  known  as  phytopathology,  or  plant  pathology. 
A  study  of  the  bacteria  constitutes  bacteriology.    A  considera- 
tion of  the  useful  or  harmful  aspects  of  plants  is  included 
under  the  general  term  economic  botany,  and  under  this  head 
there  are  such  subdivisions  as  agricultural  and  horticultural 
botany.  These  are  but  the  leading  aspects  under  which  plants 
may  be  studied. 

It  is  evident  that  these  divisions  have  no  sharply  marked 
lines  between  them,  and  that  they  are  not  all  made  upon  the 
same  basis.  For  example,  we  might  study  the  bacteria  as 
shown  in  their  structure,  which  would  be  morphology ;  or  as 
shown  in  their  relation  to  disease,  which  would  be  pathology ; 
or  in  their  relation  to  farm  and  garden  crops,  which  would  be 
economic  botany. 

146.  Names  of  plants  and  groups  not  most  important.  It  is 
impossible  to  study  plants  in  any  extended  way  without  hav- 
ing definite  names  for  them  and  their  parts,  as  well  as  for  the 
different  kinds  of  work  that  they  do.    We  need  names  of  the 
different  people  whom  we  know  in  order  that  we  may  speak 
of  them  in  a  definite  way.    If  we  had  not  these  names  we 
should  constantly  have  to  use  long  descriptions  that  would 


160  PRACTICAL  BOTANY 

be  inconvenient  and  confusing.  How  plants  live  and  the  rela- 
tions that  they  bear  to  other  living  things  are  the  really  im- 
portant things,  and  though  names  are  quite  necessary,  we  must 
keep  clearly  in  mind  that  they  are  merely  tools,  by  means  of 
which,  in  our  thinking  and  speaking,  we  may  easily  handle 
plants.  There  are  two  great  pieces  of  work  that  plants  do,  as 
has  been  made  evident  in  the  preceding  chapters :  plants  must 
have  ways  of  securing  and  using  the  needed  food  materials,  — 
they  must  attend  to  the  needs  of  nutrition ;  and  they  must 
attend  to  the  establishment  of  succeeding  generations  of  their 
kind,  —  the  work  of  reproduction.  All  that  plants  do  may  in 
some  way  be  related  to  one  or  both  of  these  two  great  pieces 
of  work.  Protection  through  the  winter  seasons  and  drought, 
and  responses  to  the  conditions  of  life  in  water  or  in  tropical 
regions  are  in  some  way  related  to  nutrition  and  reproduction. 
While,  therefore,  we  shall  study,  in  some  of  the  following 
chapters,  a  few  representatives  of  the  great  groups  of  plants, 
we  shall  always  have  to  keep  in  mind  that  what  we  really 
want  to  find  out  is  what  plants  are,  how  and  where  the  differ- 
ent groups  live,  how  their  habits  of  living  are  related  to  the 
life  of  other  living  things,  and  how  they  reproduce  themselves. 


CHAPTER  XI 
THE  BACTERIA  (SCHIZOMYCETES) 

147.  Introductory.    In  the  preceding  chapter  it  was  stated 
that  the  thallophytes  constitute  one  of  the  four  great  divisions 
of  the  plant  kingdom.    They  are  plants  of  very  simple  struc- 
ture, and  do  not  have  roots,  stems,  and  leaves.    Some  of  them 
are  extremely  simple,  one-celled  plants,  and  others  are  very 
large  and  quite  conspicuous.    In  methods  of  producing  their 
offspring  thallophytes  are  also  comparatively  simple.    Of  all 
the  thallophytes  the  bacteria  are  simplest  in  structure,  and  we 
shall  consider  them  first  in  the  series  of  plant  groups.1 

What  the  bacteria  are  and  how  they  live  are  questions  of 
very  great  hygienic  as  well  as  botanical  importance.  Bacteria 
have  sometimes  been  represented  as  wholly  dangerous  to  men, 
a  conception  very  far  from  true.  They  have  been  called  germs, 
microbes,  bacilli,  and  microorganisms,  often  without  any  defi- 
nite notions  as  to  the  real  meaning  of  these  names.  Even  the 
fact  that  they  are  plants  is  not  generally  recognized  by  the 
public,  though  for  many  years  scientists  have  known  it.  What 
the  bacteria  are,  how  they  live,  and  how  their  life  affects  the 
life  of  other  living  things  are  some  of  the  questions  to  be 
discussed  in  this  chapter. 

148.  Form.  There  is  variation  in  the  form  of  bacteria,  as 
there  is  among  higher  plants.   Three  groups,  classed  accord- 
ing to  form,  are  generally  recognized, —  the  spherical  (coccus), 
rod  (bacillus,  Fig.  150),  and  spiral  {spirillum)  groups.  There  are 
sphere  forms  of  wide  difference  in  sphericity,  rod  forms  with 

1  Cultural  experiments  offer  a  better  means  of  laboratory  study  of  the 
bacteria  than  does  microscopic  work.  Demonstration  microscopes  will  be 
found  helpful,  however,  in  giving  an  idea  of  the  size  and  form  of  a  few  of 
the  common  types  of  bacteria. 

161 


162 


PRACTICAL  BOTANY 


great  variations  in  length  and  diameter,  and  spiral  forms  hav- 
ing from  a  fraction  of  one  spiral  to  many  spirals.  Further- 
more, spherical  forms  may  become  piled  upon  one  another 
so  that  colonies  result,  and  rods  may  be  joined  (Sect.  152)  in 


FIG.  150.  A  group  of  bacteria 

A,  Bacillus  typhosus,  from  a  six-hour-old  culture  upon  nutrient  agar.  In  such 
cultures  the  main  body  of  the  bacillus  is  short  and  the  cilia  are  relatively  prom- 
inent; magnified  1000  diameters.  B,  Micrococcus  tetragenus,  three  groups  each 
of  four  individuals,  each  showing  the  characteristic  arrangement;  the  larger 
bodies  are  portions  of  the  pus  in  which  the  bacteria  occur.  C,  Bacillus  tubercu- 
losis; the  very  slender  bacilli  are  shown  among  particles  of  sputum.  D,  Proteus 
vulgaris,  a  widely  distributed  saprophytic  bacillus.  E,  Pneumococcus,  some 
individuals  of  which  have  been  inclosed  and  partially  digested  by  the  large 
white  blood  corpuscles  (phagocytes).  F,  Staphylococcus  aureus,  a  small  spheri- 
cal bacterium  usually  arranged  in  chains;  magnified  1000  diameters.  Modified 
from  Jordan's  "  General  Bacteriology  " 

such  a  way  as  to  construct  filaments.  Within  these  groups 
many  species  of  bacteria  are  known.  One  high  authority, 
Migula,  considers  that  there  are  1272  distinct  species  of  bac- 
teria, most  of  which  belong  to  the  bacillus  type. 


THE  BACTERIA  (SCHIZOMYCETES)  163 

149.  Size.   The  variations   in  size   are   even  greater  than 
those  in  form.  The  average  bacillus  type  of  bacterium  is  about 

fftfhnr mch  (i  oV o  mmO  in  diameter  and  T ^ ^ o  inch  (w o  mmO 
in  length.  The  spherical  bacteria  have  an  average  diameter 
slightly  less  than  that  of  the  average  bacillus  forms,  while 
most  spiral  forms  are  larger.  There  are  known  forms  that  are 
yery  much  smaller  than  these  averages.  It  is  indeed  thought 
by  some  bacteriologists  that  the  failure  to  discover  the  bacteria 
that  produce  certain  diseases  is  due  to  our  inability,  even  by 
means  of  the  most  powerful  microscopes,  to  see  these  organ- 
isms. It  is  suggestive  in  this  connection  to  state  that  the 
organism  which  produces  yellow  fever  (perhaps  an  animal 
organism  and  not  a  bacterium  at  all)  is  small  enough  to  pass 
through  the  pores  of  a  compact  porcelain  filter.1 

If  the  average  bacteria  are  -%-%^-Q-Q  inch  in  diameter  and  y-Q ^^ 
inch  in  length,  and  if  such  bacteria  were  placed  upon  one 
another  end  to  end  compactly  until  a  pile  one  inch  long,  one 
inch  high,  and  one  inch  wide  was  constructed,  the  cubic-inch 
mass  would  contain  6,250,000,000,000  individual  bacteria. 
This  is  approximately  65,000  times  the  number  of  human  be- 
ings in  the  United  States.  Or,  assuming  that  a  man's  finger 
nail  is  -^  inch  (i-  mm.)  in  thickness,  by  placing  one  upon  an- 
other, end  to  end,  to  make  a  single  stack  of  average  bacteria 
as  high  as  the  finger  nail  is  thick  would  require  no  less  than 
200  bacteria. 

150.  Structure.  These  are  extremely  simple  plants,  and  are 
believed  by  some  to  be  structurally  the  simplest  known  living 
things.    The  wall  of  the  cell  is  often  made  up  of  a  slime-like 
sheath.    In  some  bacteria  this  wall  is  a  distinctly  gelatinous 
capsule.    It  is  not  of  cellulose  material,  as  it  is  in  the  higher 
plants.    Internally  the  cell  structure  is  quite  simple,  consisting 
of  structures  that  are  thought  to  be  cytoplasm  and  granules 
of  nucleus-like  material. 

Many  bacteria  have  been  observed  to  have  long  hair-like 
flagella  extending  from  or  through  the  cell  wall  (Fig.  150). 
1  Reed  and  Carroll,  American  Medicine,  1902,  p.  301. 


164  PRACTICAL  BOTANY 

Sometimes  these  are  present  in  sufficient  numbers  to  cause  the 
entire  cell  to  have  a  woolly  appearance.  In  other  cases  but 
one  or  a  few  of  these  flagella  are  present.  These  are  organs 
of  locomotion. 

151.  Motility.  Many  kinds  of  bacteria  can  move  from  place 
to  place  by  means  of  the  hair-like  flagella.    The  rate  of  their 
movement,   which  varies   greatly,   may  be  strikingly  rapid. 
"  The  typhoid  bacillus  may  travel  a  distance  of  4  mm.  (about 
J  inch),  or  about  2000  times  its  own  length,  in  one  hour ;  the 
cholera  spirillum  may  attain  for  short  distances  a  speed  of 
18  cm.  (about  7  inches)  per  hour,"  l  a  speed  that  is  45  times 
as  great  as  that  of  the  typhoid  bacillus.     There  are  other 
spirillum  forms  that  move  with  great  rapidity.     These  dis- 
tances may  seem  short,  but  if  put  in  terms  of  the  actual  length 
and  bulk  of  the  organism,  they  become  more  significant.    If  a 
man  should  travel  as  many  times  his  own  length  as  the  typhoid 
bacillus  or  as  the  cholera  spirillum  (assuming  that  the  cholera 
spirillum  is  of  length  similar  to  the  typhoid  bacillus,  though 
it  really  does  attain  a  much  larger  size),  how  far  would  he 
travel  in  one  hour? 

152.  Reproduction.  The  usual  method  of  reproduction  is  by 
fission,  in  which  the  bacterial  cell  divides  into  two  new  cells, 
each  of  which  is  a  new  individual.     The  newly  formed  cells 
usually  separate  soon  after  being  formed.    Sometimes,  how- 
ever, they  continue  to  divide  for  a  number  of  generations 
without  becoming  separated,  thus  producing  a  chain  or  fila- 
ment of  plants.    In  a  very  short  time  the  new  plants  become 
full-grown  and  ready  again  to  divide.    In  the  case  of  some 
kinds   of   bacteria  newly  formed   individuals  divide  within 
twenty  minutes  to  a  half  hour  after  they  themselves   are 
produced.     Thus  two  or  three  generations  may  be  formed 
within  an  hour's  time.    The  possibilities  of  this  rate  of  repro- 
duction are  enormous.    If  all  conditions  were  to  remain  en- 
tirely favorable  for  reproduction,  a  bacterium  which  divides 
but    once    an   hour  would   in  two    days   produce    offspring 

1  Jordan,  E.  O.,  General  Bacteriology,  1908,  pp.  59-60. 


THE  BACTERIA  (SCHIZOMYCETES)  165 

numbering  281,500,000,000,  and  "  in  three  days  the  progeny 
of  a  single  cell  would  balance  148,356  hundredweight."  l  Of 
course  it  is  well  known  that  ordinarily  this  rate  of  reproduc- 
tion cannot  be  realized,  because  growth  conditions  do  not 
remain  favorable.  The  food  supply  is  soon  exhausted,  and 
the  excretions  from  the  bacteria  themselves  render  conditions 
unfavorable.  But  in  situations  where  bacteria  can  grow  they 
really  do  reproduce  themselves  and  increase  their  number 
with  astonishing  rapidity.  The  possibilities  of  production  and 
growth  of  large  numbers  are  evident  when  we  keep  in  mind 
that  for  a  considerable  time  many  millions  of  bacteria  could 
live  in  a  cubic  inch  of  milk  or  beef  broth. 

In  another  kind  of  reproduction  that  is  found  in  but  a 
few  of  the  bacteria  the  interior  of  the  bacterial  cell  becomes 
rounded  and  inclosed  by  a  relatively  heavy  wall.  This  heavy- 
walled  body  may  remain  inactive  for  a  long  period,  and  upon 
the  return  of  favorable  conditions  may  again  produce  the  kind 
of  cell  which  formed  it.  Such  specially  made  reproductive 
cells  are  called  spores.  They  often  serve  to  preserve  bacteria 
through  periods  of  unfavorable  conditions,  —  as  drought,  lack 
of  proper  air,  absence  of  suitable  food,  and  unfavorable  tem- 
perature. Some  kinds  can  withstand  freezing  or  boiling  tem- 
peratures. It  is  much  more  difficult  to  destroy  bacteria  that 
produce  spores  than  those  which  have  only  the  usual  growing 
structures.  There  are  very  few  spore-forming  bacteria  among 
those  that  produce  diseases  of  men.  This  is  fortunate  for  men, 
since  the  problem  of  combating  disease  would  be  much  more 
complex  if  all  our  disease-producing  bacteria  should  possess 
these  resistant  spores. 

An  illustration  of  bacterial  spore  action  is  seen  in  the  disease 
known  as  anthrax.  Sometimes  sheep,  cattle,  rats,  mice,  and 
other  animals,  as  well  as  men,  are  killed  within  a  very  short 
time  —  a  few  hours  to  a  few  days  —  by  this  disease.  Before 
adopting  the  method  of  treatment  devised  by  Louis  Pasteur, 
France,  in  single  years,  had  lost  as  much  as  $20,000,000 
1  Jordan,  E.  O,.,  General  Bacteriology,  1908,  p.  61. 


166  PEACTICAL  BOTANY 

worth  of  cattle  and  sheep.  The  spores  form  only  when  the 
bacteria  are  exposed  to  the  air.  When  an  animal  dies  of  an- 
thrax, if  its  body  decays  while  exposed  to  the  air,  millions  of 
anthrax  spores  are  formed.  These  spores  can  lie  in  the  field 
for  very  long  periods,  probably  several  seasons,  and  withstand 
the  variations  in  temperature,  moisture,  and  light.  Under  ordi- 
nary conditions  these  will  not  germinate  until  they  are  intro- 
duced into  the  body  of  an  animal,  when  they  again  begin  their 
growth. 

153.  Nutrition.  Bacteria  absorb  their  food  material  directly 
through  the  walls  of  their  cells.    Living,  as  they  do,  within 
or  upon  their  food  supply,  direct  contact  with  it  is  secured. 
Most  kinds  of  bacteria  live  upon  organic  foods.    The  sources 
of  this  food  are  as  numerous  as  are  the  kinds  of  organic  sub- 
stances in  the  universe,  —  living  and  dead  bodies  of  plants 
and  animals,  plant  and  animal  products,  materials  in  solution 
in  water,  materials  in  the  air  and  the  soil.    Some  bacteria1 
thrive  without  free  oxygen  and  thus  can  live  upon  food  ma- 
terial in  places  where  other  organisms  cannot  live.    A  few 
bacteria  can  construct  food  somewhat  as  the  green  plants  do. 

It  must  also  be  noted  that  bacteria,  like  other  living  things, 
produce  and  excrete  substances  that,  if  retained,  would  be  in- 
jurious to  them.  If  excreted  and  accumulated  about  the  bac- 
teria in  great  quantity,  these  substances  would  soon  kill  them. 
If  a  jar  of  beef  broth  is  carefully  sealed  after  any  ordinary 
bacteria  have  been  introduced  into  it,  there  will  at  first  be  a 
rapid  increase  in  their  number  and  the  liquid  will  become 
clouded  with  the  organisms  and  their  products.  But  the 
excretions  soon  accumulate  to  such  an  extent  that  the  bac- 
teria can  no  longer  grow.  They  become  dormant  or  die  and 
settle  to  the  bottom  of  the  jar  or  collect  in  a  jelly-like  mass 
at  the  surface. 

154.  Relation  to  decay.  The  bacteria  and  certain  other  de- 
pendent organisms  (as  molds,  yeasts,  many  animals),  while 
living  upon  the  bodies  or  the  products  of  plants  and  animals, 

1  Known  as  anaerobic  species. 


THE  BACTERIA  (SCHIZOMYCETES)  167 

use  parts  of  them  as  food.  The  processes  of  securing  this  food 
result  in  partial  or  complete  breaking  down  of  the  food  sub- 
stance. This  is  known  as  decay.  While  a  body  is  undergoing 
decay,  usually  several  kinds  of  bacteria  and  other  organisms 
live  in  turn  upon  it.  In  complete  decay  all  of  the  nutrient 
organism  is  used  as  food,  passes  into  the  air  as  gases,  or  is 
dissolved  in  water  and  carried  into  the  earth  or  into  streams. 
The  materials  that  result  from  decay  are  not  only  directly  the 
remnants  of  the  original  plant  or  animal  body,  but  may  also 
contain  excretions  from  decay-producing  organisms.  Further- 
more, many  of  these  organisms  of  decay  have  themselves  died 
and  decayed. 

Processes  of  decay  are  of  great  biological  importance.  It  is 
necessary  to  have  the  dead  bodies  and  the  waste  products  of 
living  bodies  of  plants  and  animals  reduced  to  a  form  that 
makes  their  removal  possible.  The  materials  that  are  broken 
down  are  thus  made  usable  for  future  growth  of  plants  and 
animals.  Without  decay,  all  usable  food  material  would  even- 
tually be  rendered  unavailable  for  further  growth  of  plants 
and  animals,  so  that  life  on  the  earth  would  cease.  The  earth's 
supply  of  food  materials  would  be  locked  up  in  organized  plant 
and  animal  bodies. 

155.  Relation  to  agriculture  and  gardening.  It  has  long  been 
known  that  the  introduction  of  decayed  and  decaying  organic 
matter  into  soils  enables  them  to  sustain  a  more  luxuriant 
vegetation.  Undecayed  organic  matter  is  not  available  for 
those  plants  which  we  usually  desire  to  grow.  Such  material 
must  await  more  complete  disorganization  before  it  can  be 
useful.  It  is  desirable  to  regulate  decay  so  that  the  largest 
possible  amount  of  its  products  may  be  retained  in  the  soil. 
This  is  one  of  the  problems  of  scientific  agriculture.  For  ex- 
ample, if  stable  manure  in  large  masses  is  allowed  to  "  heat " 
under  the  rapid  destructive  action  of  the  bacteria  and  other 
living  things  which  flourish  in  it,  much  valuable  ammonia  is 
given  off  into  the  atmosphere  and  lost.  Slower  decay,  espe- 
cially if  underground,  wastes  but  little  ammonia.  The  bacteria 


168  PRACTICAL  BOTANY 

are  of  great  importance  to  agriculture  and  gardening  in  other 
ways,  but  these  are  considered  in  the  chapters  Further  Dis- 
cussion of  Dependent  Plants  and  Further  Discussion  of  Plant 
Industries. 

156.  Relation  to  other  industries.  It  is  impossible  to  do  more 
in  this  connection  than  to  suggest  a  few  of  the  industries  in 
which  bacterial  processes  have  an  important  part.  The  number 
and  extent  of  the  changes,  physical,  chemical,  or  both,  that 
always  occur  when  bacteria  grow,  suggest  the  immense  indus- 
trial field  that  lies  before  the  student  of  bacteriology ;  for  bac- 
teria may,  under  favorable  circumstances,  grow  upon  almost 
any  organic  substance.  In  this  immense  field  there  is  as  yet 
but  a  small  amount  of  positive  knowledge.  There  are,  how- 
ever, a  few  cases  in  which  some  of  the  facts  are  known.  From 
general  knowledge  and  from  what  has  already  been  said,  it  is 
evident  that  all  our  fruits,  vegetables,  meats,  etc.,  are  at  times 
in  danger  of  destruction  by  bacteria  or  other  organisms.  How 
to  prevent  this  destruction  has  been  one  of  the  important  prob- 
lems since  civilization  began.  Surplus  production  of  food  is 
useless  unless  some  of  it  may  be  kept  for  future  needs.  If  men 
could  not  preserve  foods,  they  could  live  only  in  regions  where 
there  is  perpetual  food  production,  or  they  must  constantly 
migrate  into  regions  where  food  might  be  had. 

In  preservation  of  fruits  much  progress  has  been  made  by 
improvements  in  methods  of  gathering  them.  Most  fruits  have 
a  natural  covering,  which,  if  unbroken  or  unbruised,  and  kept 
clean,  will  for  a  long  time  prevent  the  entrance  of  organisms 
of  decay.  If  two  sets  of  ripe  apples  are  gathered,  one  carelessly 
so  that  bruising  and  scratching  of  the  surface  occurs,  the  other 
with  sufficient  care  to  avoid  these  things,  and  both  are  placed 
upon  a  shelf  in  the  schoolroom,  an  interesting  demonstration 
will  be  made  of  the  desirability  of  care  and  cleanliness. 

Low  temperature  and  drying  were  found  to  prevent  decay 
long  before  it  was  known  how  decay  is  produced.  Refrigeration 
has  now  become  a  leading  method  of  preventing  decay,  since 
bacteria  do  not  thrive  at  or  below  the  freezing  temperature. 


THE  BACTERIA  (SCHIZOMYCETES)  169 

Foods  are  thereby  kept  for  years,  and  shipped  all  over  the 
earth.  Drying  is  proportionately  less  used  than  formerly,  since 
this  process  causes  most  foods  to  lose  some  desirable  qualities. 
Destructive  organisms  cannot  thrive  upon  thoroughly  dry  food. 
Dried  fruits,  dried  meats,  and  dried  grains  (a  natural  process 
of  preservation)  may  be  kept  for  years.  Preservation  in  salt 
and  sugar  or  their  strong  solutions  serves  the  same  purpose  as 
drying,  since  salt  and  sugar  have  such  avidity  for  water  that 
destructive  organisms  have  their  protoplasmic  water  extracted 
and  therefore  cannot  grow.  Fish,  beef,  pork,  and  other  meats 
may  be  preserved  by  thoroughly  smoking  with  wood  smoke. 
The  creosote  that  is  carried  into  the  meat  by  this  process  helps 
to  prevent  the  growth  of  destructive  organisms.  This  method 
of  preservation,  though  thoroughly  wholesome,  requires  long 
exposure  to  the  smoke.  It  is  not  so  extensively  used  for  beef 
and  pork  as  formerly,  though  large  quantities  of  fish  are  still 
preserved  in  this  manner. 

Sterilization  and  canning  have  recently  offered  very  great 
opportunities  for  food  preservation  and  shipment.  By  means 
of  heat  properly  applied  all -bacteria  and  other  organisms  of 
decay  may  be  killed.  If  such  thoroughly  sterilized  food  is 
hermetically  sealed  in  vessels  that  have  been  similarly  steri- 
lized, it  will  not  decay.  It  is  difficult,  but  entirely  possible,  to 
sterilize  thoroughly  both  food  and  sealing  appliances  so  that 
absolutely  no  organism  will  grow.1  Other  methods  of  preser- 
vation by  introduction  of  chemicals  that  prevent  growth  of 
bacteria  are  sometimes  used.  These  chemical  preventives  are 
poisons.  If  eaten  by  men  in  very  small  quantities,  injurious 
results  are  not  immediately  noticeable,  but  their  use  is  at- 
tended by  constant  danger.  Milk,  meats,  and  confections  that 
are  so  preserved  should  always  be  avoided. 

1  Sometimes  in  canned  goods,  stale  meats,  and  other  foods,  poisonous 
ptomaines  are  formed.  They  are  probably  secretions  from  bacteria,  results 
of  chemical  change  or  decay  of  such  foods  as  meats  and  fruits,  or  originate 
from  the  disorganization  of  bacteria.  For  means  of  prevention,  see  "Care 
of  Food  in  the  Home,"  Farmers'  Bulletin  375,  U.  S.  Dept.  Agr.,  1909. 


170  PRACTICAL  BOTANY 

The  relation  of  bacteria  to  milk  and  water  supply  is  a  sub- 
ject of  great  importance.  A  rather  large  number  of  harmless 
bacteria  may  often  be  found  in  reasonably  pure  milk  and  water ; 
but  careless  handling  of  bottles  and  cans,  or  the  use  of  tuber- 
culous cows,  may  result  in  widespread  disease,  and  has  been 
known  to  cause  epidemics  of  tonsilitis,  scarlet  fever,  and  ty- 
phoid fever.  If  milking  is  done  through  absorbent  cotton  or 
several  layers  of  cheesecloth,  used  as  a  cover  for  the  milk  pail, 
most  of  the  impurities  are  caught  therein.  Milk  pails  and  ship- 
ping cans  should  always  be  sterilized  before  they  are  used. 
Milkmen  who  otherwise  were  fairly  careful  in  their  work  have 
been  known  to  rinse  their  pails  and  cans  in  polluted  wells  or 
streams.  Bacteria  of  various  diseases  have  thus  been  distrib- 
uted. Either  milk  or  water  may  be  sterilized  by  boiling,  and 
may  be  kept  so  if  placed  in  sterile  vessels.  Both,  however, 
are  better  if  they  can  be  secured  and  kept  in  a  pure  con- 
dition without  it.  An  efficient  method  of  preserving  milk  is 
by  Pasteurization,1  in  which  the  vessels  containing  the  milk 
are  placed  in  water  and  brought  to  a  temperature  of  150°  to 
155°  F.,  and  then  cooled  and  kept  cool  until  used.  This  method 
kills  most  of  the  bacteria  in  milk  and  makes  less  change  other- 
wise than  does  boiling.2 

The  formation  of  acetic  acid  (the  acid  of  vinegar)  is  due 
to  the  growth  of  several  kinds  of  bacteria.  Part  or  all  of  the 
processes  of  curing  tobacco,  tanning  of  leather,  preparation 
of  plant  fibers  as  flax  and  hemp,  butter  and  cheese  making, 
and  many  other  important  industries  depend  upon  the  growth 
processes  of  different  kinds  of  bacteria. 

1  "Directions  for  the  Home  Pasteurization  of  Milk,"  Circular  152,  Bureau 
of  Animal  Industry,  U.  S.  Dept.  Agr.,  1909. 

2  "Care  of  Milk  on  the  Farm,"  Farmers'  Bulletin  63,  U.  S.  Dept.  Agr., 
1906. 

"Bacteria  in  Milk,"  Farmers'  Bulletin  348,  U.  S.  Dept.  Agr.,  1909. 

"  Sources  of  Bacteria  in  Milk,"  Bulletin  51,  Storrs  Agr.  Ex.  Sta.,  Storrs, 
Conn.,  1908. 

"  Milk  and  its  Products  as  Carriers  of  Tuberculosis  Infection,"  Bulletin  148, 
Bureau  of  Animal  Industry,  U.  S.  Dept.  Agr.,  1909. 


THE  BACTERIA  (SCHIZOMYCETES)  171 

157.  Relation  to  diseases  of  planjts  and  animals.  Growth  of 
bacteria  within  other  plants  and  in  animals  often  results  in 
disease  of  the  host  organism.  Types  of  plant  diseases  that  are 
caused  by  bacteria  are  the  crown  galls  produced  upon  roots  of 
apples,  peaches,  and  pears;  also  cucumber  wilt,  and  soft  rot 
of  cabbage.  Many  diseases  of  animals  are  caused  by  bacteria, 
as  hog  cholera,  tuberculosis  of  cattle,  and  anthrax  or  splenic 
fever.  It  was  in  connection  with  the  study  of  animal  dis- 
eases that  the  causal  relation  of  bacteria  was  first  conclusively 
proved.  Bacteria  were  discovered  almost  two  hundred  years 
before  it  was  proved  that  they  cause  diseases.  Indeed,  a  good 
deal  was  known  about  the  nature  of  these  diseases  before  it 
was  known  that  they  are  caused  by  bacteria.  Means  were 
finally  devised  for  isolating  and  growing  alone  many  kinds  of 
bacteria,  and  then  by  the  introduction  of  certain  kinds  into 
susceptible  animals  definite  kinds  of  disease  resulted. 

Very  brief  reference  to  two  kinds  of  bacterial  disease  will 
afford  illustrations  of  some  effects  produced  upon  plants  and 
animals  by  disease-producing  bacteria.  In  the  case  of  black 
rot  of  cabbage  the  bacteria  enter  the  cabbage  leaf  through 
the  leaf  pores.  Once  within  the  leaf,  they  grow  rapidly,  and 
brown  or  black  spots  appear  on  the  leaf  as  outward  evidence 
of  the  inward  ravages  of  the  bacteria.  These  leaves  may 
become  shriveled.  The  disease  may  spread  throughout  the 
plant  and  result  in  destruction  of  the  entire  head  of  cabbage. 
The  organisms  of  decay  may  follow  the  bacteria  which  pro- 
duce the  disease. 

In  the  disease  known  as  anthrax,  already  referred  to  in 
Sect.  152,  when  active  anthrax  bacteria  or  their  spores  are 
introduced  into  the  alimentary  tract  of  cattle  or  sheep,  they 
find  their  way  into  blood  vessels,  where  they  grow  with  sur- 
prising rapidity.  In  most  cases  the  death  of  the  host  animal 
occurs  within  a  few  hours  to  a  few  days  from  the  time  of 
infection.  If  the  dead  body  decays  in  an  exposed  place,  the 
anthrax  bacteria  or  their  spores  may  soon  become  a  means  of 
new  infection  and  the  death  of  other  animals. 


172  PRACTICAL  BOTANY 

158.  Relation  to  diseases,  of  man.  In  the  section  on  nutri 
tion  of  the  bacteria  (Sect.  153)  attention  was  directed  to  the 
fact  that  excretions  are  regularly  produced  by  them.  In  case 
of  disease-producing  forms  some  of  these  excretions  are  inju- 
rious or  poisonous,  and  are  known  as  toxins.  In  susceptible 
plants  or  animals  toxins  may  produce  disease.  Each  kind 
of  disease-producing  bacteria  forms  its  own  peculiar  toxin  or 
toxins,  which  in  time  produce  particular  kinds  of  disease. 
Substances  that  neutralize  toxins  or  their  effects  are  known 
as  antitoxins.  The  diseased  organism  tends  to  manufacture 
these  "  anti-bodies,"  or  antitoxins,  which,  when  formed  in 
sufficient  quantities,  counteract  the  influence  of  the  toxins. 
In  some  cases  (smallpox,  diphtheria),  when  one  has  had  a 
disease  and  has  produced  sufficient  antitoxin  to  enable  him  to 
overcome  the  attack,  he  is  usually  not  again  susceptible  to 
this  particular  disease.  He  is  immune.  Some  people  are  natu- 
rally immune  to  certain  diseases.  There  are  diseases  (such  as 
mumps,  measles,  scarlet  fever,  diphtheria,  smallpox)  against 
which  most  people  may  acquire  immunity  by  once  surviving 
an  attack.  This  immunity  is  usually  lifelong,  though  excep- 
tions are  known.  In  the  case  of  other  diseases  (typhoid,  in- 
fluenza), one  is  soon  susceptible  to  another  attack. 

Smallpox  vaccination1  consists  in  infecting  human  beings 
with  bacteria  that  have  been  grown  in  such  unfavorable  ways 
that  their  ability  to  produce  the  disease  is  greatly  reduced. 
Consequently  the  result  of  vaccination  is  to  cause  a  very  mild 
attack,  which,  however,  is  strong  enough  to  produce  immunity 
against  fully  virulent  smallpox.  This  lasts  for  a  period  of 
years  (usually  given  as  seven  years),  though  the  protective 
effect  gradually  diminishes. 

In  the  case  of  diphtheria  it  has  been  found  possible  to  secure 
from  horses  and  mules  an  antitoxin  that  will  counteract  diph- 
theria toxins  in  the  human  body.  These  animals  are  naturally 
immune  to  diphtheria,  but  by  injecting  into  their  bodies  toxins 
produced  in  beef  broth  by  diphtheria  bacteria,  this  natural 

1  The  specific  bacteria  which  produce  smallpox  have  not  been  identified. 


THE  BACTERIA  (SCHIZOMYCETES)  173 

immunity  is  greatly  increased.  First  into  the  animal's  body 
there  is  injected  a  small  amount  of  toxin.  This  process  is 
repeated,  with  an  increasing  amount,  at  intervals  of  a  week 
or  a  little  less,  for  a  period  of  two  or  three  months.  The  ani- 
mal finally  withstands,  with  no  ill  consequences,  an  amount 
of  toxin  that  would  have  proved  fatal  if  used  at  first.  At  this 
time  some  of  the  blood  is  drawn  off,  allowed  to  clot,  and  the 
antitoxic  serum  is  sterilized.  After  its  relative  strength  is 
determined,  it  is  sealed  in  small  bottles  and  is  ready  for  dis- 
tribution. A  human  being  who  has  diphtheria  may  then  be 
given  the  proper  amount  of  antitoxin.  If  it  is  properly  given, 
and  given  early  enough,  the  attack  is  defeated.1 

Great  benefits  have  come  to  the  human  race  through  the 
discovery  of  diphtheria  antitoxin.  It  was  generally  introduced 
in  1894.  A  study  of  the  following  table,  containing  data  for 
ten  years  before  and  ten  years  after  the  introduction  of  anti- 
toxin, will  give  an  idea  of  the  value  of  this  scientific  discovery. 

AVERAGE  ANNUAL  DEATH  RATE  FROM  DIPHTHERIA 
PER  10,000  POPULATION  2 

BEFORE  USE  OF         ANTITOXIN 
ANTITOXIN  PERIOD 

(1885-1894)  (1895-1904) 

Paris.     .     ."".     .     .     .     .     .-.'•'.     .     .          6.41  .     .     .  1.49 

Berlin .     .     ;     fitfS  .     .     .  2.95 

Vienna 8.14  ...  2.95 

London 4.85  $&J&i  3.88 

New  York  .     .    ,*:..*•.•«;...-#,::>     .     .     .15.19  ,  ..,.-=  ..  6.62 

Boston    .     .•:.•'.     .    . '.....    ....     .11.76  ...    .,    ..  6.34 

Baltimore '.     .   '.  ". \".  ''•''.     7M  V    .     .  4.99 

Chicago8 /    .     .14.29  .     .     .  5.13 

An  estimate  of  the  number  of  lives  saved  annually  in  New 
York  and  Chicago  will  further  illustrate  the  benefits  from  the 
use  of  antitoxin. 

1  Certain  disastrous  cases  where  impure  antitoxin  was  used,  resulting  in 
infecting  patients  with  other  disease  germs,  are  inexcusable.    These  cases, 
however,  should  not  lead  people  to  decline  to  use  antitoxin. 

2  Jordan,  E.  O.,  General  Bacteriology,  1908. 

3  Use  of  antitoxin  begun  in  1895-1896 ;  drop  from  12.01  (1895)  to  7.62  (1896). 


174  PRACTICAL  BOTANY 

159.  Watercourses   as  means  of  distribution  of  bacteria  of 
disease.   As  may  be  expected,  water  courses  are  means  of  dis- 
tribution of  some  kinds  of  bacteria.    To  what  extent  this  is 
true  for  all  kinds  is  not  known,  but  in  case  of  the  typhoid 
bacteria  there  has  been  much  conclusive  investigation.    The 
following  illustration  is  one  of  a  number  that  might  be  cited. 
The  southern  part  of  New  Hampshire  and  the  northern  part 
of  Massachusetts  are  drained  by  the  Merrimac  River.     In  the 
region  thus  drained  are  many  industrial  cities  and  towns.    In 
1890-1891  there  occurred  in  this  region  a  great  epidemic  of 
typhoid  fever.   The  water  of  the  Merrimac  River  and  its  trib- 
utaries was  the  means  of  carrying  away  the  sewage  for  the 
entire  region,  and  the  cities  of  Lowell  and  Lawrence,  which 
took  their  water  supply  from  this  river,  took  sewage-polluted 
water.    The  cities  of  Concord,  Nashua,  and  Haverhill  did  not 
get  their  water  from  the  Merrimac.    The  epidemic  began  in 
Lowell,  and  this  was  soon  followed  by  a  more  severe  epidemic 
in  the  city  of  Lawrence,  situated  downstream  from  Lowell. 
There  is  a  small  stream,  Stony  Brook,  which  flows  through  a 
suburb  of  Lowell  and  empties  into  the  Merrimac  three  miles 
above  the  point  at  which  the  Lowell  water  supply  was  taken. 
The  first  cases  of  typhoid  were  along  Stony  Brook,  and  these 
cases  polluted  the  water,  thus  in  turn  polluting  the  supply  for 
the  main  part  of  Lowell.    Furthermore,  the  Lowell  sewers 
entered  the  Merrimac  nine  miles  above  the  water  intake  for 
Lawrence,  and  thus  polluted  the  water  supply  so  that  typhoid 
fever  was  well  distributed  throughout  those  parts  of  Lawrence 
where  this  water  was  used. 

The  other  cities  in  this  same  valley  had  very  little  typhoid 
fever,  while  Lowell  and  Lawrence  suffered  many  deaths, 
reaching  in  twelve  months  (1890)  187  per  10,000  population 
in  Lawrence  and  195.4  per  10,000  population  in  Lowell. 
There  are  many  such  cases  showing  the  effect  of  typhoid- 
polluted  water. 

160.  Tuberculosis:    the  great  white  plague.     The  disease 
commonly  known  as  tuberculosis  is  so  generally  distributed 


THE  BACTERIA  (SCHIZOMYCETES)  175 

and  so  destructive  that  it  has  been  called  "  the  great  white 
plague."  Its  universal  importance  demands  that  a  separate 
paragraph  be  given  to  a  brief  statement  concerning  it.  It  is 
the  most  destructive  disease  that  affects  the  human  race,  and 
in  the  United  States  it  causes  about  one  ninth  of  all  deaths. 
It  costs  the  United  States  many  hundreds  of  thousands  of 
dollars  annually,  and,  if  a  money  estimate  could  be  placed 
upon  the  many  untoward  circumstances  that  accompany  and 
follow  tuberculosis,  the  sum  would  be  appalling. 

The  tubercle  bacilli  may  infect  almost  every  part  of  the 
human  body.  Though  the  lungs  are  the  regions  most  fre- 
quently attacked,  the  bones  and  joints,  the  intestines,  the 
throat,  skin,  and  other  organs  often  are  the  regions  of  growth 
of  these  bacilli. 

The  growth  of  tubercle  bacilli  in  the  body  is  usually  very 
slow,  and  months  or  years  may  pass  before  conspicuous  con- 
sequences follow  infection.  Furthermore,  the  germs  may  live 
upon  a  handkerchief,  in  the  floor  of  a  house,  in  a  public 
building,  in  public  transportation  vehicles,  in  the  dirt  of  the 
street,  etc.,  for  a  very  long  time,  and  then  grow  when  they 
are  introduced  into  the  human  body.  Some  of  the  lower  ani- 
mals (cattle,  hogs,  poultry,  etc.)  are  subject  to  tuberculosis, 
and  while  there  seems  to  be  some  doubt  whether  it  is  of  exactly 
the  same  kind  as  tuberculosis  of  human  beings,  the  dangers 
are  such  that  careful  disposition  should  be  made  of  all  tuber- 
culous animals. 

The  usual  source  of  infection  is  through  the  organs  of 
breathing,  though  the  germs  may  be  carried  into  the  mouth 
and  other  organs  by  means  of  milk  and  other  food.  Since  the 
dried  or  partially  dried  tubercle  bacilli  may  be  transported  by 
the  air,  it  is  evident  that  the  greatest  precaution  should  be 
taken  to  keep  the  air  from  becoming  contaminated  with  these 
germs.  Furthermore,  it  is  known  that  when  tubercle  bacilli 
are  moist,  the  direct  light  of  the  sun  has  a  destructive  effect 
upon  them,  and  that  fresh  air  is  likely  to  contain  fewer 
tubercle  bacilli  than  the  "  close  "  air  of  rooms  in  which  many 


176  PRACTICAL  BOTANY 

people  have  been.  Plenty  of  fresh  air,  sunshine,  and  whole- 
some food  are  most  important  factors  in  preventing  attacks 
of  tuberculosis,  and  these,  together  with  good  general  vitality 
of  the  body,  are  one's  best  guaranty  against  this  disease.  On 
the  other  hand,  poor  food,  bad  air,  dark  rooms,  and  low  vital- 
ity render  the  body  a  favorable  growing  place  for  these  disease 
germs  when  once  they  are  introduced.  These  predisposing 
factors  are  of  tremendous  importance  in  relation  to  tubercu- 
losis, and  too  much  emphasis  cannot  be  given  them.  The 
nature  of  the  occupation  and  habits  of  men  have  much  to  do 
with  predisposing  and  exposing  them  to  tuberculosis.  This 
was  proved  by  an  Englishman  named  Newsholme,  in  1898, 
when  by  means  of  records  he  showed  that  for  each  100  agri- 
culturists who  died  from  tuberculosis  and  other  respiratory 
diseases,  there  were  453  potters  and  earthenware  workers,  407 
cutters,  373  plumbers,  and  335  glassmakers  who  died  from 
these  same  diseases.  At  a  time  when  so  much  is  known  about 
how  to  prevent  tuberculosis  it  seems  a  needless  waste  of  human 
life  to  allow  so  many  people  to  become  affected  by  it. 

161.  Prevention  of  disease.  Bacteria  are  distributed  into  al- 
most every  nook  and  corner  of  the  earth,  —  in  soil,  air,  water, 
dust,  and  upon  and  within  the  bodies  of  plants  and  animals. 
Disease-producing  bacteria  are  common,  though  less  abun- 
dantly distributed  than  forms  which  do  not  cause  disease. 
A  good  deal  is  known  regarding  the  methods  of  distribution 
and  infection  of  the  most  dangerous  disease-producing  forms, 
though  our  knowledge  is  by  no  means  complete.  Polluted 
water  and  milk  have  often  been  the  means  of  wholesale  dis- 
tribution of  typhoid  germs  (Fig.  151).  The  house  fly  is  one 
of  the  most  dangerous  agents  of  distribution  of  typhoid  and 
probably  of  other  disease  bacteria.  The  atmosphere  is  an 
efficient  means  of  carrying  bacteria  of  tuberculosis.  They 
must,  however,  be  dry  in  order  that  they  may  be  thus  carried. 
Every  possible  effort  should  be  made  to  remove  the  breed- 
ing places  of  flies  (refuse  from  stables,  exposed  and  decaying 
sewage,  etc.)  and  to  keep  them  out  of  public  and  private 


THE  BACTERIA  (SCHIZOMYCETES) 


177 


dwelling  places ;  to  insure  a  pure  and  well-kept  supply  of  milk 
and  water ;  to  keep  vegetables  and  other  foods  that  are  handled 
in  public  places  free  -from  dust  and  flies  and  promiscuous 
fingering ;  thoroughly  to  disinfect  all  known  or  suspected 


FIG.  151.    A  chart  illustrating  the  number  of  deaths  from  typhoid  fever 

before,  during,  and  after  the  introduction  of  improved  systems  of  sewage 

disposal  and  water  supply 

Five  prominent  cities  of  the  world  are  selected.  The  figures  indicate  the  num- 
ber of  deaths  per  each  10,000  inhabitants.  Rearranged  from  a  chart  in  Abbott's 
Hygiene  of  Transmissible  Diseases 


178  PRACTICAL  BOTANY 

disease-bearing  materials  of  all  kinds ; l  to  have  large  quan- 
tities of  fresh  air;  to  have  all  the  sunshine  possible,  for  sun- 
shine is  destructive  of  many  disease  germs.2 

It  is  of  great  importance  also  that  a  high  standard  of  vigor 
be  maintained  as  a  means  of  preventing  bacterial  disease. 
Many  people  have  had  disease-producing  bacteria  introduced 
into  their  bodies  without  any  serious  consequences,  indeed 
without  even  being  conscious  of  danger.  Their  bodies  were 
in  such  vigorous  condition  that  the  initial  growth  of  bacteria 
was  prevented.  An  instructive  experiment  relative  to  this 
point  was  performed  by  Pasteur.  Ordinary  domesticated  fowls 
are  not  readily  susceptible  to  anthrax.  Pasteur  found,  how- 
ever, that  if  he  kept  the  fowls  at  lower  temperatures  than  was 
normal  for  them,  they  were  very  susceptible  to  anthrax  and 
that  under  such  circumstances  it  proved  deadly  to  them.  This 
is  a  common  principle  in  hygiene.  When  through  excessive 
fatigue,  loss  of  proper  sleep  or  nourishment,  or  for  any  other 
reason,  bodily  vigor  is  greatly  reduced,  susceptibility  to  disease 
is  increased. 

Modern  bacteriology  has  offered  the  human  race  the  means 
of  escape  from  many  diseases.  Ignorance,  lack  of  care,  and 
financial  greed  are  often  the  only  excuses  that  can  be  offered 
when  certain  diseases  occur.  If  only  those  who  are  responsible 
for  them  might  be  attacked  by  these  preventable  diseases,  the 
matter  would  not  be  so  serious,  for  in  that  case  disease  and 
the  resulting  deaths  would  tend  to  eliminate  those  who  do 
not  act  upon  the  knowledge  of  sanitation  which  we  now 

1  In  Bacteria,  Yeasts,  and  Molds  in  the  Home,  by  H.  W.  Conn  (Ginn  and 
Company),  there  is  an  excellent  popular  discussion  of  the  nature  of  bacteria 
and  the  effects  of  their  growth. 

2  In  Germany  it  is  unlawful  for  filtered  water  to  contain  more  than  100 
bacteria  per  cubic  centimeter,  and  it  should  always  contain  less.    Boston 
has  a  legal  standard  which  requires  that  market  milk  shall  not  contain  more 
than  500,000  bacteria  per  cubic  centimeter;  and  Rochester,  New  York,  and 
Milwaukee,  Wisconsin,  have  legal  standards  of  250,000  per  cubic  centimeter. 
Some  kinds  of  certified  milk  may  contain  less  than  10,000  Jbacteria  per  cubic 
centimeter.  On  the  other  hand,  in  impure  milk  the  number  may  run  from 
several  hundreds  of  thousands  to  several  millions. 


THE  BACTEEIA  (SCHIZOMYCETES)  179 

possess.  This,  however,  is  a  public  matter,  and  innocent  people 
must  now  suffer  from  the  lack  of  precaution  of  others.1 

162.  Classification.  The  thallophytes  are  divided  into  the 
fission  plants  (schizophytes),  the  algae,  and  the  fungi.  The 
fission  plants  are  divided  into  the  bacteria  (schizomycetes) 
and  the  blue-green  algae  (schizophyceae  or  cyanophyceae). 
Formerly  the  bacteria  were  included  with  the  fungi,  and  the 
blue-green  algae  with  the  algae,  but  resemblances  in  structure 
and  methods  of  reproduction  are  such  that  the  two  groups 
are  now  classed  together  as  the  schizophytes.  The  name 
means  "splitting  plants,"  or  "fission  plants,"  and  refers  to 
the  formation  of  new  individuals  by  the  division  of  the  old 
ones.  Likewise  the  technical  name  of  the  bacteria,  schizo- 
mycetes, means  "  splitting  fungi,"  or  "  fission  fungi,"  and  that 
of  the  blue-green  algae,  schizophyceae,  means  "  splitting  algae," 
or  "  fission  algae." 

The  classification  of  the  bacteria  and  the  blue-green  algae 
is  as  follows : 

Plant  Kingdom 
Thallophytes 
Schizophytes 

Class    I.    Schizomycetes  (bacteria) 

Class  II.    Schizophycese  or  Cyanophyceae  (blue-green  algse) 

1  Why  are  some  public  drinking  places  so  arranged  that  one  must  drink 
from  running  water  ?  Why  do  some  states  have  a  law  prohibiting  railway 
trains  from  carrying  public  drinking  cups  ?  What  is  the  nature  of  the  water 
supply  and  care  of  the  drinking  water  for  your  school  ? 


CHAPTER  XII 
THE  BLUE-GREEN  ALGJE  (CYANOPHYCEJB) 

163.  Introductory.  The  life  habits,  size,  and  structure  of  the 
blue-green  algae  are  such  that  we  can  obtain  the  best  notion 
of  the  whole  group  by  selecting  for  discussion  a  few  represent- 
ative plants.    "  Representative  plants  "  cannot  fully  represent 
this  or  any  other  group,  any  more  than  three  or  four  selected 
students  would  adequately  represent  an  entire  school.    How- 
ever, in  an  elementary  textbook  it  is  not  advisable  to  present 
a  large  number  of  plants  from  each  group. 

164.  Where  found.  The  blue-green  algse  are  found  in  pools 
of  stagnant  water,  along  shores  of  streams,  lakes,  and  oceans, 
in  places  where  the  water  contains  considerable  organic  matter. 
They  may  appear  as  coatings  to  sticks,  stones,  etc.,  as  float- 
ing pieces  of  dirty,  bluish-green  material,  or  as  small  masses 
free-floating  or  attached  and  held  together  in  jelly-like  balls. 
Usually  they  may  be  readily  distinguished  from  other  algae 
by  the  distinct  bluish-green  color. 

165.  Glceocapsa:  structure  and  nutrition.  In  stagnant  water 
such  as  is  found  in  old  pools,  horse  tracks  in  open  fields,  and 
sometimes  in  aquarium  jars  in  the  laboratory,  the  plant  known 
as  Gloeocapsa  may  appear  as  bluish-green  fragments  floating 
or  adhering  to  the  sides  or  bottom  of  whatever  may  contain 
the  water  in  which  it  is  growing.    These  fragments  are  made 
up  of  a  great  many  plants,  each  one  so  small  that  when  alone 
it  cannot  be  seen  without  magnification.    The  appearance  of 
the  masses  of  many  plants  may  be  thus  determined,  but  that 
of  a  single  plant  can  be  determined  only  by  the  aid  of  a  com- 
pound microscope.1   A  single  plant  when  separated  from  the 

1  In  the  first  studies  of  the  single-celled  algae  it  is  often  better  to  use  a 
good  specimen  under  a  compound  microscope  as  a  demonstration  than  to 

180 


THE  BLUE-GREEN  ALGM  (CYANOPHYCE^)      181 

others  (Fig.  152)  is  spherical  in  its  general  form.  It  has  a 
well-defined  wall,  the  cell  wall,  inside  of  which  is  the  living 
substance  of  the  plant,  the  protoplasm.  Although  in  higher 
plants  the  protoplasm  is  clearly  divided  into  different  parts, 
—  cytoplasm,  nucleus,  and  chloroplasts  (Sect.  8),  —  in  Grloeo- 
capsa  these  different  parts  are  not  evident.  The  protoplasm  of 
G-lceocapsa  is  granular,  and  there  is  a  blue-green  stain  distrib- 
uted throughout  it.  It  is  only  when  these  plants  are  massed 
together  that  the  characteristic  blue-green  color  is  seen.  In  a 
single  plant  this  coloring  matter  is 
present  in  such  small  quantities  that 
when  observed  under  a  microscope  the 
color  is  not  easily  detected. 

The  living  protoplasm  builds  the 
wall  that  surrounds  the  inner  part  of 
the  cell,  but  the  wall  itself  is  not  alive. 
Some  of  the  water  in  which  Crloeocapsa 
lives  is  absorbed  by  the  wall,  which 
causes  the  older  outer  parts  to  swell, 
thus  producing  layers  of  jelly-like 
material  around  the  protoplasm  and 
the  inner  cell  wall.  Also  through  the 
wall  the  food  material  is  absorbed. 
Even  with  the  small  amount  of  chloro- 
phyll and  blue  pigment  present  in  one  of  these  plants  photo- 
synthesis (Sect.  17)  can  be  carried  on.  Since  the  plant  lives 
in  stagnant  water,  in  which  there  is  much  decaying  organic 
matter,  it  is  not  impossible  that  it  may  absorb  and  use  directly 
as  food  some  of  these  decaying  organized  foods.  In  times  of 
drought  these  plants  may  become  dry,  although,  being  pro- 
tected by  means  of  the  heavy  gelatinous  covering,  they  dry 
very  slowly,  and  when  favorable  conditions  again  come  they 
may  continue  to  grow. 

have  the  student  attempt  to  find  a  good  specimen  without  any  notion  as  to 
what  single-celled  plants  are.  Individual  studies  will  then  be  more  intelligible 
and  more  successful. 


FIG.  152.   Glceocapsa,   one 
of  the  simplest  of  the  blue- 
green  algae.  Magnified  300 
times 

A-E,  successive  changes  in 
the  development  of  new  in- 
dividuals from  a  parent  cell 


182 


PRACTICAL  BOTANY 


166.  Glceocapsa:  reproduction.   After  a  G-lceocapsa  plant  has 

been  growing  for  a  time  it  may  divide  into  two  new  plants. 

The  wall  divides,  completing  the  separation  of  the  protoplasm 

...  into  two  cells  and  thus  two  new 

plants    are   formed   (Fig.  152). 
The  separation  of  the  protoplasm 
really  begins  before    the  walls 
push  inward,  but  this  protoplas- 
mic division  cannot  readily  be 
observed.      The   new 
plants,     before     they 
'•/  become  free  from  the 

mass  of  jelly  inclosing 
them,  may  again  re- 
produce themselves, 
so  that  four,  eight,  or 
even  a  much  larger 
number  may  be  united 
in  one  colony.  In  such 
cases  the  plants  are 
held  together  so  very 
closely  that  they  of- 
ten do  not  assume  the 
spherical  form. 

Each  new  Gloeocapsa 
plant  is  essentially  the 
kind  that  its  parent 
was  before  the  divi- 
sion occurred.  In  fact 
the  parent  plant  by 
division  becomes  di- 
rectly two  new  indi- 
viduals. This  method  of  reproduction  by  division  or  fission 
(splitting)  is  the  simplest  known  in  the  plant  kingdom,  and 
is  characteristic  of  the  simplest  animals  as  well  as  of  the  sim- 
plest plants. 


FIG.  153.  Nostoc 

At  the  left  (A)  are  several  of  the  Nostoc  balls,  which 
appear  as  glistening,  rounded  masses  (natural  size). 
At  the  right  (Z>),  inclosed  in  gelatinous  material, 
are  a  few  chains  of  Nostoc  plants  which  have  been 
taken  from  one  of  the  balls  and  greatly  magnified. 
In  the  chains  several  of  the  enlarged  heterocysts 
may  be  seen 


THE  BLUE-GKEEN  ALG^E  (CYANOPHYCE^E)      183 

167.  Nostoc:  structure  and  nutrition.  In  regions  such  as 
those  mentioned  as  the  living  place  of  Crloeocapsa^  and  also 
upon  damp  soil  or  floating  upon  standing  water,  there  may 
be  found  the  jelly-like  balls  of  Nostoc.  Instead  of  the  rather 
ragged  fragments  of  the  Crloeocapsa  masses,  Nostoc  usually  is 
found  in  irregularly  rounded  compact  balls  (Fig.  153,  A), 
which  have  a  dark  bluish-green  color.  The  ball  is  a  colony 
of  plants,  but  when  it  is  taken  in  the  fingers  no  evidence  of 
the  existence  of  single  plants  can  be  obtained. 

Under  magnification  the  ball  is  seen  to  be  composed  of 
granular  jelly,  through  which  are  interwoven  thousands  of 
chains  of  cells,  each  of  which  is  a  Nostoc  plant.  Usually  two 
kinds  of  cell  are  found  in  the  chain,  one  or  more  larger  ones 
called  Jieterocysts  (which  simply  means  "  different  cells  "  ),  and 
ordinary  cells  (Fig.  153,  J5),  each  one  resembling  a  G-loeocapsa 
plant.  These  ordinary  cells  of  Nostoc  manifest  an  evident  dif- 
ference from  those  of  G-loeocapsa;  the  jelly-like  mass  about 
Nostoc  plants  is  not  in  layers  about  each  cell,  as  is  true  in 
Crloeocapsa.  The  cells  are  loosely  held  together  in  chains  by 
attachments  of  their  walls,  thus  making  a  slightly  more  com- 
plex plant  than  Crloeocapsa. 

In  nutrition,  Nostoc  may  absorb  directly  through  the  cell  walls 
the  materials  that  are  needed  for  photosynthesis,  or  it  may,  per- 
haps, absorb  organized  foods,  since  much  food  of  this  kind  is  in 
the  water  in  which  the  plants  live.  Since  the  jelly  mass  is  often 
quite  large,  obviously  there  must  be  absorbed  through  the  outer 
part  of  the  Nostoc  ball  the  food  needed  not  only  for  the  outer- 
most plants  but  also  for  those  that  are  more  deeply  situated. 

In  times  of  drought  the  gelatinous  nature  of  the  Nostoc  balls 
results  in  extremely  slow  drying,  though  if  the  drought  be  long- 
continued  the  whole  ball  may  become  so  dry  as  to  crumble  be- 
tween the  fingers.  Even  when  as  dry  as  this,  not  all  of  the 
plants  are  killed,  and  a  large  number  of  them  proceed  to  grow 
when  furnished  the  needed  moisture.  This  covering  of  jelly 
and  the  consequent  slow  drying  seems  to  be  of  the  greatest 
importance  in  the  life  of  both  Nostoc  and  Crloeocapsa. 


184  PRACTICAL  BOTANY 

168.  Nostoc:  reproduction.  If  a  single  Nostoc  cell  is  sepa- 
rated within  the  mass  from  the  chain  in  which  it  has  grown, 
it  soon  divides  in  essentially  the  same  way  as  does  the  Crloeo- 
capsa  plant;  but  in  the  case  of  Nostoc,  the  new  cells  thus 
formed  are  likely  to  remain  together,  and  will  redivide  in  the 
same  direction  as  did  the  cell  at  first,  and  thus  form  a  new 
chain.   Nostoc  is  not,  however,  usually  reproduced  by  one  cell's 
becoming  free  and  behaving  as  just  described.    Divisions  of 
the  cells  do  occur  as  stated,  sometimes  all  or  nearly  all  of  the 
cells  of  a  chain  dividing  at  the  same  time.    This,  if  contin- 
ued, would  soon  produce  a  plant  of  great  length,  —  a  result 
which  does  sometimes  occur.    Usually,  however,  in  one  or 
more  cells  of  the  chain  the  protoplasm  dies  and  the  cell  wall 
greatly  enlarges,  thus  producing  a  heterocyst.    This  hetero- 
cyst  apparently  weakens  the  connection  between  the  adjoin- 
ing cells,  and  the  chain  separates  at  this  point,  the  heterocyst 
usually  adhering  to  one  of  the  new  chains  (Fig.  153,  Z?).    The 
presence  of  two  or  more  heterocysts  may  result  in  breaking 
the  chain  of  cells  into  three  or  more  new  Nostoc  chains  at  the 
same  time.    This  Wgd  of  reproduction  resembles  that  which 
wls  seen  in  G-lceocapsa,  in  as  much  as  the  cells  divide  to  repro- 

vdiice  the  plant.    It  differs  in  the  fact  that  new  plant  chains  are 
formed  by  an  additional  reproductive  structure,  the  heterocyst. 

169.  Oscillat oria :  structure  and  nutrition.  In  the  same  kind 
of  regions  in  which  Grloeocapsa  and  Nostoc  are  found,  but  more 
abundant  and  more  widely  distributed,  is  the  plant  Oscillatoria. 
Oscillatoria  filaments  grow  together,  sometimes  forming  mats 
of  a  dark  green,  dirty-looking  growth.    At  times  when  a  few 
plants  are  seen  growing  free  from  others,  they  present  a  beau- 
tiful clear  green  growth  in  which  very  little  bluish  coloring 
matter  can  be  detected.    The  mats,  though  often  slimy,  are 
not  covered  by  the  masses  of  gelatinous  substance  that  are 
seen  in  the  two  preceding  forms. 

Some  of  the  Oscillatoria  plants  are  so  large  that  if  placed  in 
a  dish  of  water  they  may  be  studied  in  a  general  way  without 
magnification.  They  are  thread-like  plants,  the  length  of  each 


THE  BLUE-GKEEN  ALG^  (CYAKOPHYCE^)     185 


individual  greatly  exceeding  its  thickness.  Some  of  them  per- 
form a  peculiar  swinging  or  oscillating  movement,  from  which 
the  generic  name  Oscillatoria  is  taken.  They  may,  however, 
move  forward  as  well  as  sidewise. 

Under  a  compound  microscope  Oscillatoria  is  seen  to  con- 
sist of  a  great  many  cells  held  very  closely  together  in  a 
common  tubular  sheath  (Fig.  154).  If  free  from  the  sheath, 
one  of  the  cells  assumes  the 
spherical  form.  But  normally 
the  cells  are  compressed  so 
closely  in  the  sheath  that  the 
separate  walls  appear  as  one 
common  wall.  A  plant  there- 
fore consists  of  many  of  these 
cells  held  together  in  a  common 
wall.  It  may  grow  in  length  by 
having  the  cells  divide,  which 
they  regularly  do. 

As  compared  with  Gloeocapsa 
and  Nostoc,  Oscillatoria  contains 
a  great  deal  of  chlorophyll, 
which  may  be  much  or  little 
obscured  by  blue  coloring  mat- 
ter. It  lives  in  water,  often  at 
the  outlets  of  sewers  and  drains,  or  upon  damp  surfaces,  from 
which  it  absorbs  the  needed  materials  for  the  construction  of 
foods.  It  grows  vigorously,  being  able  to  thrive  throughout 
a  wide  range  of  temperature  and  other  climatic  conditions. 

170.  Oscillatoria :  reproduction.  Division  of  cells  in  this  plant 
does  not  necessarily  mean  reproduction  of  the  individual,  but 
may  signify  merely  its  growth.  A  single  Oscillatoria  cell  may, 
if  free,  grow  until  it  has  reproduced  a  plant  similar  to  the  one 
from  which  it  came.  This  is  not,  however,  its  usual  method 
of  reproduction.  In  a  long  specimen  usually  one  or  more  cells 
die,  thus  weakening  the  sheath  that  holds  the  cells  together. 
This  allows  the  plants  to  break  at  these  points,  and  each  piece 


FIG.  154.  Oscillatoria 

A,  tips  of  several  plants;  B,  part  of 

one  plant  enlarged  to  show  cellular 

structure.    Both  magnified,  B  much 

more  than  A 


186  PEACTICAL  BOTANY 

that  is  set  free  is  a  new  plant  and  may  continue  to  grow  until 
it  assumes  the  proportions  of  the  old  one.  This  is  essentially 
the  same  kind  of  reproduction  that  is  seen  in  Nostoc,  except 
that  here,  instead  of  having  a  heterocyst,  the  dead  cell  does 
not  become  enlarged.  Oscillatoria  plants  may  also  break  at  any 
point  to  produce  new  individuals. 

171.  General  characteristics  of  the  blue-green  algae.  In 
addition  to  the  types  of  blue-green  algae  that  have  been  dis- 
cussed, many  other  kinds  are  abundant.  They  are  found  in 
the  same  kinds  of  regions  as  those  that  have  been  presented 
in  the  preceding  paragraphs.  Members  of  this  group  have  the 
characteristic  blue-green  color,  with  this  color  pretty  evenly  dis- 
tributed throughout  the  interior  of  the  cells.  The  blue-green 
algae  are  extremely  simple  in  structure,  being  one-celled  plants 
(as  G-lceocapsa),  or  plants  made  up  of  cells  arranged  in  rows 
so  as  to  form  simple  chains  (as  Nostoc),  or  filaments  (as  Oscil- 
latoria). Some  of  the  members  of  the  group  are  more  complex 
than  Oscillatoria,  as  Grloeotrichia  and  Rivularia,  which  are  com- 
monly found  as  small,  glistening,  jelly-like  balls  attached  to 
sticks  and  to  the  stems  of  other  plants.  They  are  usually 
found  in  shallow  fresh-water  lakes,  or  sometimes  free-floating. 
The  entire  group  consists  of  plants  that  are  relatively  simple 
in  form  Und  structure.  The  cells  are  simple,  and  definitely 
organized  chloroplasts  are  not  present.  Nuclei  of  the  kind 
known  in  the  other  algee  and  in  the  higher  plants  have  not 
been  demonstrated  in  this  group,  although  fragments  that 
resemble  the  nuclei  of  higher  plants  have  been  found. 

Most  of  the  members  of  the  group  have  a  jelly-like  cover- 
ing, and  in  many  forms  this  holds  the  plants  together  in  colo- 
nies. This  covering  seems  to  be  of  advantage  to  the  plants 
during  periods  of  drought  by  regulating  the  rate  of  drying. 

The  water  or  moist  habitat  and  the  simplicity  of  structure 
suggest  the  simple  way  of  securing  food  material,  namely  by 
absorbing  it  directly  through  any  part  of  the  wall  of  the  plant. 
By  means  of  chlorophyll,  members  of  this  group  may  manu- 
facture foods  through  the  process  known  as  photosynthesis. 


THE  BLUE-GREEN  ALG.E  (CYANOPHYCE^E)      187 

New  plants  are  established  by  the  blue-green  algae  in  the 
simplest  ways  that  are  possible.  Reproduction  takes  place  by 
means  of  fission  of  the  single-celled  forms,  or  by  the  breaking 
into  two  or  more  parts  of  the  chains  or  filaments  of  the  less  sim- 
ple forms.  Sometimes  in  certain  species  of  Nostoc  reproduction 
is  said  to  occur  by  means  of  a  special  heavy  -walled  cell  which, 
after  lying  quiet  for  a  time,  may  grow  into  a  new  plant. 

The  growing  plant  is  often  spoken  of  as  the  vegetative 
plant,  and  when  reproduction  occurs  as  it  does  in  the  blue- 
green  algae,  by  division  to  produce  new  plants,  the  process  is 
known  as  vegetative  reproduction.  Such  reproduction  is  charac- 
teristic of  the  blue-green  algae. 

The  blue-green  algae  have  a  very  wide  distribution.  They 
are  found  in  both  fresh  and  salt  waters,  in  warm  and  cool  tem- 
peratures, and  at  high  and  low  altitudes.  They  thrive  in  water, 
and  also  upon  land,  provided  they  have  a  supply  of  moisture. 
Many  of  them  are  most  luxuriant  near  the  mouths  of  sewers, 
in  case  light  and  temperature  conditions  are  favorable.  In  re- 
gions where  moisture  is  intermittent  they  thrive  part  of  the  year 
and  are  dormant  the  rest  of  the  time.  Often  they  grow  in  such 
numbers  as  to  tinge  the  water  with  green,  or  whatever  other 
color  the  plant  may  have.  Fresh-water  lakes  are  often  distinctly 
green  from  the  growth  of  Rivularia,  GrloBotrichia,  and  other 
forms.  The  Red  Sea  owes  its  hue  to  the  abundant  growth  of  a 
reddish-brown  member  of  this  group.  The  margins  of  some  of 
the  pools  about  geysers  and  lakes  in  the  Yellowstone  National 
Park,  and  shores  of  lakes  and  streams,  are  often  so  colored. 

172.  Classification  of  the  Fission  Plants  (Schizophytes): 

Thallophytes 
Schizophytes 

Class  I.   Schizomycetes  (bacteria) 

Illustrated  by  numerous  type  forms  and  various  methods  of 

living 

Class  II.   Schizophycese,  or  Cyanophycese  (the  blue-green  algae) 
Leading   genera   used    as    illustrations,  —  Glceocapsa,   Nostoc, 
Oscillatoria 


CHAPTER  XIII 
THE  GREEN  ALGJE  (CHLOROPHYCEJE)  AND  OTHER  ALGJE 

173.  General  considerations.  The  green  algae  are  found  in 
almost  all  inland  waters,  floating  freely  upon  the  surface,  ly- 
ing in  heavy  mats  near  or  below  the  surface,  forming  masses 
upon  the  bottom,  and  often   attached  to  various  solid  sub- 
stances in  the  water.    A  few  are  marine  in  habit.    They  are 
widely  and  abundantly  distributed  and  may  be  found  by  any 
observing  student.     Not  infrequently  they  are  spoken  of  as 
"  pond  scums,"  "  water  mosses,"  and  "  seaweeds." 

Usually  it  is  easy  to  distinguish  green  algae  from  most 
other  algae  by  the  fact  that  in  members  of  this  group  the 
chlorophyll  is  not  obscured  by  any  other  coloring  matter. 
Various  shades  of  green  are  presented  in  different  plants,  and 
indeed  in  the  same  kinds  of  plants  at  different  growth  periods, 
but  the  color  is  not  readily  confused  with  that  of  the  other 
groups. 

174.  Pleurococcus:  structure  and  habitat.   This  green  alga 
grows  in  great  abundance  upon  the  partially  shaded  portions 
of  trees,  fences,  rocks,  and  old  buildings,  and  when  moist  it 
presents  the  appearance  of  a  coating  of  green  paint.    Some- 
times it  is  called  "  green  slime."    It  adheres  so  closely  to  the 
object  upon  which  it  grows  that  few  people  recognize  it  as  a 
plant.    It  is  one  of  the  most  widely  distributed  of  all  plants. 

When  examined  under  suitable  magnification  it  is  seen  that 
the  green  slime  is  composed  of  thousands  of  single-celled 
plants,  each  so  small  that  as  a  separated  individual  it  is  not 
visible  to  the  ordinary  observer  (Fig.  155).  A  careful  meas- 
urement of  a  number  of  plants  showed  their  average  diameter 
to  be  about  -$$$-$  of  an  inch  (.014  mm.).  In  other  words,  if 
a  row  of  these  plants  side  by  side  should  be  arranged  across 

188 


THE  GKEEN  A.LGM  (CHLOEOPHYCE^E)         189 


the  unsharpened  end  of  an  ordinary  lead  pencil,  approximately 
500  plants  would  be  required  to  complete  the  row.  How 
many  would  be  required  to  occupy  one  cubic  inch  ? 

Each  plant  is  somewhat  spherical  and  has  a  well-defined 
cell  wall.  Within  this  wall  is  the  protoplasm,  which  is  colored 
green  by  the  chlorophyll.  The  chlorophyll  is  usually  confined 
to  a  special  part  of  the  protoplasm,  this  part  being  called  the 
chloroplast,  which  means  "  a  body  which  bears  chlorophyll." 
Often  it  is  not  possible  to  distin- 
guish the  chloroplasts  in  Pleura- 
coccus^  the  chlorophyll  appearing  to 
be  evenly  distributed  throughout 
the  plant.  The  nucleus  is  another 
special  part  of  the  protoplasm.  It 
is  a  mass  of  protoplasm  denser 
than  the  other  portions,  usually 
lies  near  the  center  of  the  cell,  and 
is  a  structure  of  great  importance 
in  the  activities  of  the  plant. 

When  chloroplasts  are  evident 
it  is  possible  also  to  see  about 
them  a  thin,  almost  colorless,  pro- 
toplasmic substance,  the  cytoplasm. 
A  single  Pleurococcus  plant,  there- 
fore, consists  of  the  cell  wall  and 
the  protoplasm  that  is  contained  by  this  wall.  The  protoplasm 
may  be  divided  into  chloroplasts,  cytoplasm,  and  nucleus.  In 
some  cases,  also,  there  may  be  seen  vacuoles,  which  are  regions 
within  the  cell  surrounded  by  cytoplasm  but  containing  air 
or  cell  sap. 

175.  Pleurococcus:  nutrition.  The  protoplasm  of  this  plant 
contains  chlorophyll,  and  if  carbon  dioxide  and  water  are  ob- 
tainable it  can  carry  on  photosynthesis.  Carbon  dioxide  may 
be  secured  from  the  air.  The  bark,  or  other  support  upon 
which  the  plants  grow,  is  often  sufficiently  moist  to  enable 
Pleurococcus  to  obtain  water  from  it.  Rains  and  heavy  dew 


FIG.  155.  Green  slime  (Pleuro- 
coccus) 

a,  single  plants  showing  cell  wall, 
granular  cytoplasm,  and  nucleus ; 

b,  plants  in  process  of  reproduc- 
tion by  division  or  fission ;  c  and 
d,  further  divisions  sometimes  re- 
sulting in  formation  of  colonies 

of  plants.   Greatly  enlarged 


190  PRACTICAL  BOTANY 

supply  water  more  or  less  intermittently.  Possibly  water 
may  be  absorbed  directly  from  a  moist  atmosphere.  If  dry 
bark  with  Pleurococcus  on  its  surface  is  placed  within  a  moist 
bell  jar,  the  plants  soon  become  bright  green,  thus  indicating 
that  they  are  at  work. 

Heat,  cold,  and  the  extreme  drought  either  of  summer  or  of 
winter  are  some  of  the  great  extremes  which  this  plant  must 
undergo  in  order  to  live.  Exposed  as  it  is,  it  nevertheless  is 
able  to  pass  through  such  periods  and  grow  luxuriantly  within 
a  short  time  after  the  return  of  favorable  conditions.  If  in 
zero  weather  Pleurococcus  is  brought  into  the  laboratory  and 
moistened,  within  a  few  hours  it  begins  to  grow. 

176.  Pleurococcus:  reproduction.  Pleurococcus  cells  divide, 
thus  forming  new  plants  directly,  as  has  been  seen  to  occur  in 
Grloeocapsa.  This  vegetative  reproduction  in  favorable  weather 
results  in  a  rapid  multiplication  of  the  plants.  Divisions  follow 
one  another  in  such  a  way  that  whole  colonies,  the  descendants 
of  one  individual,  are  often  found  grouped  together  (Fig.  155). 

Sometimes,  in  near  relatives  of  Pleurococcus  that  live  in  the 
water,  another  kind  of  reproduction  occurs.  Within  the  cell 
wall  the  protoplasm  divides  so  as  to  form  several  (eight,  six- 
teen, or  thirty-two)  small  bodies.  Each  of  these  has  a  nucleus 
and  cytoplasm  which  are  obscured  by  chlorophyll,  an  extremely 
thin  cell  wall,  and  two  small  hair-like  extensions,  the  cilia  (sin- 
gular, cilium).  After  a  time  the  old  plant  wall  breaks,  and 
these  bodies,  by  means  of  the  active  cilia,  begin  to  swim  about 
in  the  water.  Soon  they  become  quiet,  the  cilia  are  lost  or  are 
withdrawn  into  the  main  body  of  the  cell,  and  the  cell  begins 
to  grow  and  develop  into  a  new  plant  like  the  one  that  formed 
it.  Thereafter  it  may  reproduce  itself  vegetatively  or  by  the 
process  just  described. 

These  cells  that  are  specially  made  for  the  work  of  repro- 
duction are  called  spores.  In  the  study  of  other  kinds  of 
plants  we  shall  find  several  kinds  of  spores ;  and  while  they 
may  differ  in  .the  ways  in  which  they  are  formed,  they  are  alike 
in  that  all  may  reproduce  the  kinds  of  plants  that  form  them. 


THE  GREEN  ALG^  (CHLOROPHYCE^)         191 


Spores  that  have  special  structures  by  means  of  which  they 
swim  are  called  zoospores,  meaning  "animal  spores,"  or  "mov- 
ing spores."  They  were  thus  named  when  it  was  supposed  that 
self -caused  movement 
is  a  distinguishing  fea- 
ture of  animals. 

Plants  which  have 
swimming  spores  have 
means  of  more  ready 
distribution  than  do 
those  that  reproduce 
entirely  by  means  of 
fission. 

177.  Spirogyra:  its 
habitat  and  structure. 
The  algse  commonly 
spoken  of  as  "pond 
scums"  are  found  in 
standing  water,  often 
floating  upon  its  sur- 
face. One  of  the  most 
abundant  of  these  is 
Spirogyra.  Within  the 
water,  it  appears  as 
long  threads  of  a  clear 
green  color,  at  times 


-n 


FIG.  156.  Spirogyra 

ch,  the  spirally  arranged  chloroplast;  n,  the  nu- 
cleus which  is  supported  by  the  bands  of  cyto- 
plasm (c?/) ;  cytoplasm  also  appears  just  within  the 
cell  wall.  The  central  cavity  of  the  cell  is  usually 
occupied  by  one  or  more  large  vacuoles.  At  the 
right  are  two  cells  of  one  plant.  At  the  left  are 
parts  of  two  plants  whose  cells  have  conjugated 
to  form  zygospores  (Z).  Greatly  enlarged 


attached  by  one  end  to 
some  support;  when 
floating  upon  the  sur- 
face of  the  water,  it 
commonly  appears  in 
yellowish-green  mats 
in  which  are  many 
bubbles  of  gas  or  air.  It  is  soft  like  silk,  and  may  thus  be 
distinguished  from  most  other  algae  likely  to  be  found  in 
similar  places. 


192  PKACTICAL  BOTAKY 

When  magnified,  the  cells  that  compose  Spirogyra  are  seen 
to  be  very  large  as  compared  with  those  of  any  alga  yet  stud- 
ied. They  are  joined  end  to  end,  thus  forming  the  filamentous 
plant.  Each  cell  has  a  cylindrical  cell  wall  which  contains 
one  or  more  peculiar  spirally  arranged  chloroplasts,  each  of 
which  extends  almost  or  quite  the  entire  length  of  the  cell 
(Fig.  156).  Different  species  of  Spirogyra  may  have  different 
numbers  of  chloroplasts  in  each  cell,  and  this  is  one  of  the 
ways  of  distinguishing  the  species  from  one  another.  If 
the  chloroplast  were  uncoiled,  it  would  be  like  a  ribbon  with 
the  edges  more  or  less  indented.  A  layer  of  cytoplasm  lies 
just  within  the  wall,  and  the  cytoplasmic  threads  run  from 
all  sides  to  the  nucleus,  which  the  cytoplasm  surrounds.  Much 
of  the  interior  of  the  cell  is  occupied  by  one  or  more  vacuoles. 
The  cytoplasmic  layer  and  the  nucleus  may  be  made  more 
conspicuous  by  mounting  the  plants  in  an  iodine  solution, 
which  pulls  the  cytoplasm  away  from  the  cell  wall  and  also 
stains  the  nucleus  and  the  threads  which  support  it. 

178.  Spirogyra:  nutrition.  The  supply  of  water  for  this  plant 
is  secured  from  the  surrounding  medium  in  which  are  dissolved 
the  carbon  dioxide  and  other  inorganic  materials  from  which 
foods  are  made.  Indeed  there  is  much  water  within  the  plant. 
By  carefully  drying,  it  may  be  demonstrated  that  sometimes 
as  much  as  98  per  cent  of  Spirogyra  is  water.  That  photo- 
synthesis is  carried  on  is  often  made  evident  by  the  oxygen 
bubbles  that  arise  from  the  active  plants.  It  is  possible  to 
collect  the  oxygen  that  is  produced  by  alga)  approximately,  as 
shown  in  Fig.  12.  A  test  tube  is  placed  over  the  small  end 
of  a  glass  funnel,  both  being  under  water  in  order  to  exclude 
all  air  from  them.  While  under  water  the  large  end  of  the 
funnel  is  placed  over  a  mass  of  algse.  The  apparatus  is  then 
made  secure  and  left  in  an  upright  position.  As  the  plant  con- 
tinues its  work,  oxygen  bubbles  arise  and  accumulate  in  the 
closed  end  of  the  tube,  thus  forcing  out  a  similar  volume  of 
water.  The  oxygen  may  be  tested  by  the  ordinary  tests  for 
this  gas.  Because  of  the  size  and  the  length  of  this  plant,  and 


THE  GREEN  ALG^E  (CHLOROPHYCE^E)         193 

the  size  of  its  chloroplast,  it  can  expose  more  chlorophyll  to 
the  light  and  hence  do  more  photosynthetic  work  than  any 
plant  yet  studied  in  the  present  chapter. 

When  Spirogyra  cells  divide,  the  division  wall  is  at  right 
angles  to  the  length  of  the  plant.  Such  division  results  in  an 
increase  in  the  number  of  cells  and  usually  in  growth  in  length 
of  the  whole  plant.  Growth  occurs  so  rapidly  that  within  a  few 
days  after  the  plants  are  first  seen  in  the  spring  they  become  so 
abundant  that  they  may  pollute  the  water  in  which  they  grow. 


FIG.  157.  Spirogyra  in  process  of  spore  formation 

A,  conjugating  cells;  a  and  b,  conjugating  tubes;  c,  a  tube  from  a  cell  which  has 
begun  to  conjugate  with  one  that  is  already  paired ;  d,  a  second  tube  from  a 
paired  cell.  Such  secondary  tubes  rarely  develop.  B,  a  and  6,  tubes  through 
which  the  protoplasm  is  passing  to  unite  with  that  of  the  pairing  cells ;  c,  a  tube 
similar  to  c  in  A.  Greatly  enlarged 

179.  Spirogyra:  reproduction.  Plants  may  become  broken 
into  two  or  more  pieces,  and  each  piece  may  grow  into  a  sepa- 
rate plant,  thus  securing  vegetative  reproduction.  At  times, 
however,  there  occurs  a  kind  of  reproduction  quite  different 
from  any  that  we  have  as  yet  studied  in  the  algae.  The  cells 
of  two  plants  that  lie  near  one  another  unite  in  pairs,  this 
union  being  made  by  means  of  tubular  outgrowths  from  the 
pairing  cells  (Fig.  157).  These  tubes  meet  between  the  old 
cell  walls,  their  ends  fuse  and  form  a  continuous  passageway 


194  PRACTICAL  BOTANY 

from  one  cell  to  the  other.  Then  the  protoplasm  from  one 
cell  passes  through  the  tube  and  unites  with  that  from  the 
other  cell.  About  this  mass  of  protoplasm,  which  has  now  be- 
come greatly  condensed,  there  forms  a  very  heavy  cell  wall 
(Fig.  156).  This  heavy-walled  body  is  a  spore  and  may  grow 
into  a  new  plant.  It  is  formed  by  union  of  cells  and  not  by 
cell  division,  as  was  true  in  the  case  of  the  zoospores  of  plants 
related  to  Pleurococcus.  Reproduction  by  cell  union  is  sexual? 
and  by  cell  division  is  asexual.  The  spore  of  Spirogyra  is  a 
sexual  spore.  Because  it  is  formed  by  the  union  of  similar 
cells,  it  is  called  a  zygospore,  which  means  a  "yoked  spore." 
Cells  that  unite  to  form  sex  spores  are  called  gametes ;  hence 
a  zygospore  is  a  sexual  spore  that  is  formed  by  the  union  or 
conjugation  of  similar  gametes. 

Dozens  of  Spirogyra  cells  in  two  adjacent  plants  may  con- 
jugate to  produce  zygospores.  Usually  the  different  pairs  in 
the  united  filaments  will  be  found  in  about  the  same  stage  of 
spore  formation,  though  occasionally  there  will  be  some  varia- 
tion. Sometimes  the  cells  from  one  plant  will  unite  with  cells 
from  more  than  one  other  plant.  Also  occasionally  one  cell 
may  unite  with  the  adjoining  one  in  the  same  plant.  Some- 
times the  contents  of  cells  that  have  not  united  with  other 
cells  will  assume  the  form  and  characteristic  coverings  of  the 
zygospore,  and  such  spores  may  grow  into  a  new  plant. 

Zygospores  are  set  free  by  the  decay  of  the  old  cell  walls. 
After  a  period  of  rest,  as  during  drought  or  winter,  they  ger- 
minate and  produce  new  Spirogyra  plants.  It  is  of  obvious 
advantage  to  the  plant  to  have  a  heavy-walled  resting  spore 
which  will  carry  it  through  unfavorable  periods. 

180.  Cladophora:  habitat  and  structure.  Various  species 
of  Cladophora  are  found  attached  to  objects  along  shoals  in 
streams,  over  dams,  about  waterfalls,  sometimes  in  heavy 
floating  mats  along  the  margins  of  ponds,  lakes,  and  even  the 
oceans.  It  is  a  most  widely  distributed  genus,  and  one  of  the 
few  green  algse  ever  found  in  salt  waters.  Cladophora  usu- 
ally has  one  end  attached  to  some  kind  of  support,  and  is 


THE  GKEEN  ALG.E  (CHLOROPHYOE^)        195 

extensively  branched  (Fig.  158).  When  growing  vigorously, 
new  branches  are  constantly  being  formed  at  the  upper  ends  of 
some  of  the  segments.  Each 
segment  appears  to  be  one 
cell,  though  really  a  good 
many  nuclei  with  their  ac- 
companying masses  of  cyto- 
plasm are  contained  within 
each  wall.  Such  a  structure  is 
called  a  ccenocyte,  and  though 
this  same  condition  is  found 
in  another  plant  that  we  shall 
study  (Vaucheria,  Sect.  183), 
it  is  not  common  in  the  plant 
kingdom.  For  our  purpose 
we  may  think  of 
each  segment  of 
Cladophora  as  like 
one  cell.  All  of 
these  branching 
segments  may  to- 
gether compose 
a  plant  of  great 
size  as  compared 
with  the  smaller 
dimensions  of  a 
Nostoc,  an  Oscil- 
latoria,  a  Pleuro- 
coccus,  or  even  a 
Spirogyra. 

In    each    seg- 
ment   there    are 

FIG.  158.  Branching  of  Cladophora 
manv  small  cmo- 

J  After  Collins 

roplasts,  crowded 

together  so  closely  as  to  present  an  almost  solid  green  color 

even  when  viewed  under  considerable  magnification. 


196 


PRACTICAL  BOTANY 


181.  Cladophora:  nutrition.  Cladophora  is  well  supplied 
with  the  food  materials  that  it  needs.  It  grows  chiefly  in 
moving  water,  which  is  better  aerated  than  still  water.  This 


FIG.  159.  One  of  the  filamentous  algae  (Ulothrix) 

A,  the  base  of  a  plant  showing  the  attaching  or  holdfast  cell  and  a  few  vegetative 
cells ;  B,  a  group  of  vegetative  cells ;  (7,  cells  in  which  gametes  have  formed ;  D, 
two  cells  in  which  zoospores  have  formed,  and  one  cell  from  which  the  zoospores 
have  escaped;  E,  swimming  zoospores;  F,  a,  b,  c,  d,  gametes  uniting  to  form  a 
zygospore ;  G,  the  zygospore,  after  a  period  of  rest,  grows  and  finally  produces 
zoospores ;  H,  a  zoospore  germinating  to  produce  a  new  Ulothrix  plant.  All  greatly 
enlarged.  E,  F,  and  G  after  Dodel-Port 

water  also  carries  in  solution  more  or  less  inorganic  sub- 
stances from  the  soil.  The  holdfast  usually  holds  the  plant  se- 
curely in  this  favorable  environment.  Furthermore,  its  system 


THE  GREEN  ALG.E  (CHLOEOPHYCE^)         197 

of  branching  enables  it  to  expose  much  chlorophyll  to  the 
light.  Its  rapid  and  luxuriant  growth  is  evidence  that  it  is 
a  successful  plant. 

182.  Cladophora:  reproduction.  It  is  probable  that  Cladoph- 
ora  reproduces  itself  vegetatively  by  continued  growth  of 
broken  parts.  Like  Spirogyra,  it  does  not  have  any  regular 
method  of  bringing  about  vegetative  reproduction.  At  times, 
however,  in  some  of  the  segments,  the  contents  divide  into 
large  numbers  of  small  zoospores.  These  escape  from  the  old 
wall,  swim  about  for  a  time,  and  then  become  attached  and  grow 
into  new  Cladophora  plants.  This  method  of  spore  formation 
is  much  like  that  of  the  relatives  of  Pleurococcus,  except  that 
zoospores  of  Cladophora  are  formed  in  much  greater  numbers, 
by  a  special  cell  rather  than  by  the  whole  plant,  and  under  con- 
ditions suited  to  abundant  and  wide  distribution.  In  Fig.  159 
is  shown  the  method  of  reproduction  of  Ulothrix,  an  unbranched 
plant  which  in  its  reproduction  is  quite  similar  to  Cladophora. 
Plants  such  as  Cladophora  and  Ulothrix  have  still  another 
method  of  reproducing  themselves.  At  times  the  cells,  in- 
stead of  forming  zoospores,  form  bodies  which  are  like  the 
zoospores  in  form  and  movement,  but  smaller.  It  seems  that 
one  of  these  alone  cannot  reproduce  the  plant,  or,  if  it  should 
germinate,  it  produces  a  plant  that  does  not  live.  It  is  not 
a  spore,  since  it  cannot  directly  reproduce  the  plant  which 
formed  it.  Two  of  these  bodies  may  unite  and  form  a  cell 
which  is  capable  of  reproduction.  These  zoospore-like  bodies 
are  gametes  and  unite  to  form  a  zygospore,  which  then  pro- 
duces a  new  plant.  In  Cladophora  and  other  plants  (  Ulothrix, 
Draparnaldia,  Fig.  160)  that  reproduce  themselves  as  it  does 
there  are  interesting  suggestions  as  to  the  origin  of  sexual  re- 
production among  plants,  namely,  the  origin  of  gametes  from 
small  and  apparently  weakened  zoospores.  By  the  union  of 
these  simple  zoospore-like  gametes  there  is  formed  the  simplest 
kind  of  sex  spore,  the  zygospore.  Spirogyra  forms  its  zygospore 
in  somewhat  the  same  way  as  does  Cladophora,  but  the  process  is 
more  complex  and  no  relation  of  gametes  to  zoospores  is  shown. 


198 


PEACTICAL  BOTANY 


183.  Vaucheria:  habitat  and  structure.  Vaucheria  is  com- 
monly called  "green  felt,"  a  name  which  suggests  the  charac- 
teristic appearance  presented  by  it  as  it  grows  upon  the  moist 
surface  of  the  earth,  in  pots,  on  growing  tables  in  the  green- 
house, or  upon  damp  shaded  soil  out  of  doors.  It  also  grows 


FIG.  160.  A  branch  of  the  alga,  Draparnaldia 
After  Conn 

in  pools  of  water,  where  it  may  be  distinguished  from  many 
other  algae  by  its  coarseness.  Certain  species  of  Cladophora 
are  coarser  than  Vaucheria,  but  their  greater  length  and  more 
extensive  branching  will  ordinarily  enable  one  to  distinguish 
them.  If  the  earth  upon  which  Vaucheria  is  growing  is  exam- 
ined, the  plants  will  be  found  to  penetrate  slightly  into  the 
soil,  their  size  enabling  one  to  see  parts  of  them  without 


THE  GREEN  ALG^  (CHLOEOPHYCE^)         199 


magnification.  Plants  that  have  been  kept  in  a  closed  dish 
within  the  laboratory  for  a  few  days  grow  into  a  heavy  moss- 
like  mass  and  are  good  material  for  study. 

Under  low-power  magnification  the  whole  body  may  be 
traced  through  its  intertwining  with  its  neighbors.  It 
branches  considerably  (Fig.  161),  the  branches  arising  irreg- 
ularly and  rebranching  to  a 
small  extent.  The  newest 
branches  are  the  greenest 
and  most  active,  and  as 
they  grow  forward  older 
portions  may  die,  thus  sep- 
arating the  branches  from 
one  another  and  resulting 
in  the  formation  of  new 
individuals  by  vegetative 
reproduction.  No  cross 
walls  appear  in  the  vege- 
tative part  of  the  plant; 
hence  the  whole  plant  is  a 
ccenocyte  (Sect.  180). 

184.  Vaucheria:  nutrition. 
Water    may   be    absorbed 

from  the  earth  upon  which 

T7.       7      .  FIG.  161.  Branch  of  a  Vauchena 

Vaucherm  grows.    In  case  plant 

Of  those  Species  that  live  in  Considerably  enlarged 

the  water  the  food  supply 
is  secured  as  in  other  floating  algae.  The  abundant  chlorophyll 
suggests  considerable  ability  to  manufacture  nutrient  sub- 
stances, but  this  plant  is  not  so  well  suited  to  secure  abundant 
exposure  to  light  as  is  Cladophora.  It  is  to  be  noted  that,  living 
on  the  land  as  these  plants  often  do,  they  do  not  have  the  pro- 
tection against  extremes  of  light  and  temperature  that  water 
algae  enjoy;  also  that  in  nature  Vaucheria  plants  are  found 
in  shaded  and  otherwise  protected  places.  If  direct  sunlight 
falls  upon  these  plants  for  very  long,  they  are  not  able  to  live. 


200 


PRACTICAL  BOTANY 


185.  Vaucheria:  reproduction.  As  suggested  in  Sect.  183, 
it  sometimes  occurs  that  branches  are  left  as  separated  in- 
dividuals by  the  death 
of  the  older  portions 
of  the  plant.  This  re- 
sults in  vegetative  re- 
production. Asexual 
reproduction  may  be 
started  by  having  the 
end  of  a  branch  cut  off 
by  a  cross  wall.  The 
part  that  is  thus  cut 
off  proceeds  to  form 
an  immense  zoospore 
(Fig.  162,  ^,  5).  The 
wall  which  contains  it 
breaks,  and  it  slowly 
emerges,  and,  after  a 
period  of  separate  ex- 
istence in  the  water,  it  germinates  and  forms  a  new  plant 
(Fig.  162,  C).  This  zoospore  is  composed  of  many  cells.  It 
is  therefore  a  com- 
pound zoospore,  and 
is  coenocytic.  But  the 
compound  zoospore 
produces  only  one 
new  plant.  Forma- 
tion of  zobspores  may 
be  induced  in  the  lab- 
oratory by  keeping 
Vaucheria  plants  in  a 
dish  of  shallow  water. 
Another  kind  of  re- 
production may  occur 
at  the  same  time  that  zoospores  are  being  formed,  though  it 
usually  occurs  at  other  times.  Upon  the  sides  of  the  plant 


FIG.  162.  The  formation  of  zoospores  by 
Vaucheria 

A,  a  piece  of  a  plant  at  the  tip  of  which  a  section 
has  been  cut  off  to  produce  the  zoospore  (z) ;  B, 
a  zoospore  which  has  become  free  from  the  plant 
which  formed  it,  and  has  assumed  the  rounded 
swimming  form ;  O,  a  zoospore  germinating  to 
form  a  new  plant.  Considerably  magnified 


FIG.  163.  The  sexual  reproductive  structures 
of  Vaucheria  (V.  sessilis) 

o,  oogonia ;  A,  antheridia.  Note  the  opening  in  the 
antheridium  for  exit  of  sperms,  and  in  the  oogonia 
for  their  entrance  to  the  large  eggs.  Greatly  enlarged 


THE  GREEN  ALG.E  (CHLOKOPHYCE.E)         201 

special  short  branches  are  formed.  In  one  species  of  Vaucheria 
(V.  sessilis)  two  kinds  of  branches  arise  near  one  another 
(Fig.  163).  One  of  these  is  short  and  irregularly  spherical, 
and  has  a  beak  at  its  free  end.  This  branch  forms  one  large 
cell  within  it.  The  other  branch  is  longer,  somewhat  coiled, 
and  has  a  terminal  cell  that  is  cut  off  by  means  of  a  cross 
wall,  which  is  much  farther  from  the  main  plant  than  in  the 
other  branch.  In  the  terminal  segment  many  small  cells  are 
formed.  Through  a  small  opening  in  the  tip  of  this  coiled 
branch  these  cells  escape,  some  of  them  entering  the  beak  of 
the  other  branch,  and  one  of  them  uniting  with  the  large  ce>H. 
This  union  forms  a  spore  which  proceeds  to  develop  a  heavjr 
protecting  wall.  After  a 

period  of  rest  this  spore 

-, 
germinates  and  produces 

a  new  plant.1 

If  this  spore  had  been 

„  111  •          £       FIG.  164.  A  vegetative  cell  of  a  common 

formed  by  the  union  of  gpedes  of  cEdogonium 

similar  gametes,  we  then  Greatly  enlarged 

should  have  called  it  a 

zygospore  ;  but  it  is  formed  by  the  union  of  gametes  that  are 
very  unlike,  —  one  large  gamete,  the  egg  or  oosphere,  and  the 
other  a  small  gamete,  the  sperm,  —  and  the  resulting  spore 
is  called  an  oospore,  which  means  "egg  spore."  When  similar 
gametes  unite  to  form  a  zygospore,  the  process  is  called  conjuga- 
tion, but  when  dissimilar  gametes  unite  to  form  an  oospore,  the 
process  is  called  fertilization.  The  special  sex  organ  which 
produces  the  sperm  is  the  antheridium,  and  that  which  pro- 
duces the  egg  is  the  oogonium,  which  means  the  "egg  case." 

Vaucheria  has  three  methods  of  reproduction,  —  vegetative,, 
by  asexual  spores  (zoospores),  and  by  sexual  spores  (oospores). 

One  plant  may  use  vegetative  reproduction  at  one  period  of 
growth,  asexual  spore  reproduction  at  another,  and  sex  spore  re- 
production at  another,  but  two  methods  are  rarely  used  at  once. 

1  To  THE  TEACHER.  No  attempt  is  made  to  present  the  difficult  and  tech- 
cic&l  questions  relative  to  alternation  of  generations  in  the  thallophytes. 


202 


PRACTICAL  BOTANY 


186.  Increase  in  complexity  of  sex  organs  and  gametes.    It 

is  to  be  especially  noted  that  in  other  algae  which  we  have 

studied  reproduc- 
tive bodies  were 
formed  from  cells 
which  at  the  out- 
set were  vegeta- 
tive cells.  In  Vau- 
cheria  sex  organs 
are  made  primarily 
for  the  work  of 
reproduction,  an 
interesting  divi- 
sion of  labor  in 
the  plant.  In  some 
green  algae,  as 
(Edogonium  (Figs. 
164  and  165), 
vegetative  cells 
are  thus  formed 
into  oogonia  and 
antheridia. 

It  is  also  im- 
portant to  note 
that  in  Pleura- 
coccus  the  entire 

plant  might  divide 
A,  holdfast  cell  and  two  vegetative  cells;  B,  part  of  f  f-      i       •    f 

a  plant  in  which  are  an  oogonium  (o),  containing  egg,  eV 

and  two  groups  of  antheridia  (a),  which  have  not  yet 
formed  sperms ;  (7,  part  of  a  plant  in  which  is  an  oogo- 
nium (o),  which,  by  breaking  away  of  one  vegetative 
cell,  has  made  a  place  for  the  sperm  to  enter,  so  that  a 
fertilized  egg  or  oospore  has  been  formed,  as  is  shown 
by  its  heavy  inner  wall ;  D,  a  zoospore  of  (Edogonium, 
— D  redrawn  from  Pringsheim.  All  greatly  enlarged 


FIG.  165.  Reproduction  in  (Edogonium  nodosum 


two  new  plants ; 
or,  in  relatives 
of  Pleurococcus, 
the  entire  plant 
might  become  a 


spore  case  (spo- 
rangium), producing  zoospores.  In  Cladophora,  zoospores  are 
formed,  together  with  zoospore-like  gametes,  the  latter  uniting 


THE  GKEEN  ALG^E  (CHLOKOPHYCE^E)         203 

to  form  zygospores,  which  constitutes  the  simplest  kind  of 
sexual  reproduction.  In  Spirogyra,  zygospores  are  formed  by 
the  union  of  similar  gametes,  the  conjugation  being  brought 
about  by  siphon-like  tubes  which  unite  the  cells  from  which 
the  gametes  come.  In  Vaucheria  the  gametes  are  differentiated 
into  an  egg  and  a  sperm,  which,  by  fertilization,  produce  an 


FIG.  166.  Zygnema 

A,  two  vegetative  cells  showing  the  central  nucleus  which  lies  between  the  parts  of 
the  dumb-bell-like  chloroplast.  B,  conjugation  to  form  zygospores;  a,  6,  c,  conju- 
gating tubes ;  z,  zygospore  fully  formed.  Both  greatly  enlarged,  but  A  more  than  B 

oospore.  These  differentiated  gametes  are  found  in  specialized 
sex  organs  made  primarily  for  reproductive  work. 

187.  Other  green  algae.1  The  green  algae  are  more  abundant 
than  all  others  in  inland  waters,  and  it  is  not  possible  or  de^ 
sirable  to  mention  many  of  them  in  this  connection.  Some  of 
the  following  may  be  collected,  however,  in  regions  in  which 
those  already  discussed  are  found.  Sphcerella,  a  unicellular 

1  It  is  more  important  that  the  student  should  have  an  impression  of  the 
kinds  of  plants  found  among  the  algae  than  that  he  should  remember  names 
of  different  genera. 


204 


PRACTICAL  BOTANY 


form  somewhat  like  Pleuroeoccus,  is  frequently  found  in  stag- 
nant  water.  It  sometimes  grows  so  luxuriantly  in  barnyard 
and  roadside  pools  as  to  give  the  water  a  bright  green  appear- 
ance, and  its  resting  spores  may  impart  -a  dark  red  color  to  the 

drying  pools  in  which  the  plants 
have  flourished.  Of  the  near  rela- 
tives of  Spirogyra  there  are  several 
kinds,  some  of  which  are  Zygnema 
)P  »%.(Fig,  1£6),  Mesocarpus  (Fig.  167), 

,  and  the  desmids 
(Fig.  168).  The 
desmids  are  pe- 
culiarly fantastic 
forms,  one-celled, 
but  often  found 
in  colonies.  They 
usually  appear  in 
stagnant  waters. 
As  in  Spirogyra, 
these  plants  repro- 
duce themselves 
by  formation  of 
zygospores.  Con- 
ferva, which  re- 
sembles Ulothrix 
(see  Fig.  159),  is 
fairly  abundant  in 
ponds  and  along 
margins  of  lakes. 
Draparnaldia  is  a 

branching  form  (Fig.  160)  which  resembles  Cladophora  and 
Vaucheria  ;  Ulva,  or  sea  lettuce,  is  a  peculiar  large  salt-water 
form ;  while  Coleochcete  (Fig.  169)  is  a  disk-like  or  plate-like 
form.  Ohara,  or  stonewort  (Fig.  170),  is  a  complex  alga  that 
is  found  in  great  abundance  upon  the  bottom  of  shallow  lakes 
and  streams  throughout  the  continent.  It  has  a  heavy  coating 


FIG.  167.  Mesocarpus 

c,  conjugating  cells  which  have  bent  toward  one  another 

and  are  producing  conjugating  tubes;  p,  a  start  toward 

conjugation  with  a  third  plant.   Greatly  enlarged 


THE  GREEN  ALG^  (CHLOEOPHYCE^)         205 


of  calcareous  material,  which,  as  the  plant  dies,  falls  to  the 
bottom  of  the  pond  or  stream.  Char  a' grows  in  such  luxuri- 
ance that  its  deposits  eventually  form  deep  layers  of  this  cal- 
careous material,  or  marl  as  it  is  called.  Marl  has  been  found 
of  great  value  in  the  manufacture  of  cement,  and  not  a  few 
of  the  lakes  in  which  OJiara  grows 
are  being  dredged  to  secure  the 
marl  deposits  for  this  important 
manufacture. 

188.  Algae  and  water  supply. 
Many  of  our  large  cities  have 
found  it  advisable  to  construct 
reservoirs  for  water.  These  are 
open  pools,  lakes,  tanks,  etc., 
and  they  are  intended  to  hold 
water  enough  so  that  in  times 
of  scarcity  there  will  be  at  hand 
a  sufficient  supply.  Such  reser- 
voirs have  proved  so  admirable 
as  growing  places  for  algae  that 
these  plants  have  often  become 
a  nuisance.  Their  presence  in 
water  for  domestic  use  is  not  at- 
tractive, and,  besides,  they  may 
stop  up  the  water  pipes  ;  but  far 
more  serious  than  these  objec- 
tions is  the  actual  pollution  of 

the  water  because  of  their  pres-      A,Micrasterias;  B,B',Staurastrum 

ence.  When  they  die  they  "be-  (two  views);  c,  ciosterium.  After 
come  the  food  for  decay-produc- 
ing organisms  (Sect.  154),  and  often  positively  injurious  sub- 
stances may  thus  be  generated.  It  has  been  found  that  by  tow- 
ing about  in  such  reservoirs  a  quantity  of  copper  sulphate,1 
inclosed  in  coarse  sacking,  minute  quantities  of  the  salt  be- 
come dissolved  and  the  algse  are  thus  killed.  The  solution  is" 
not  strong  enough  to  render  the  water  unwholesome  for  use. 


FIG.  168.  Desmids 


206  PRACTICAL  BOTANY 

This  treatment  has  been  an  important  factor  in  improving  the 
water  within  reservoirs  used  as  sources  of  water  supply  for 
many  American  cities.1 

189.  The  brown  algae:  general  characteristics.  The  blue- 
green  and  the  green  algae  are  predominantly  fresh-water 
groups,  and  are  considered  the  chief  representatives  of  algae. 
The  remaining  groups,  though  almost  exclusively  salt-water 


FIG.  169.   ColeocTicete,  a  flat-bodied  green  alga,  which  is  a  single  layer  of  cells 

in  thickness.   It  sometimes  branches  extensively 

After  West 

plants,  have  such  striking  characteristics  that  brief  mention 
of  them  must  be  made,  and  pupils  who  live  near  the  seacoast 
will  be  interested  in  extending  this  study.  The  brown  algae, 
or  brown  seaweeds  (Phceophycece),  are  found  along  the  shores 
of  all  the  oceans.  They  grow  attached,  by  means  of  strong 
holdfasts,  to  rocks,  piling,  or  any  relatively  fixed  support  that 
is  available. 

1  See  ff  A  Method  of  destroying  or  preventing  the  Growth  of  Algse  and 
Certain  Pathogenic  Bacteria  in  Water  Supplies,"  and  ff  Copper  as  an  Algi- 
cide  and  Disinfectant  in  Water  Supplies,"  Bulletins  64  (1904)  and  76  (1905) 
respectively,  Bureau  of  Plant  Industry,  U.  S.  Dept.  Agr. 

Whipple,  "Microscopy  of  Drinking  Water,"  chap.  xii.  John  Wiley  &  Sons, 
New  York,  1906. 


THE  GREEN  ALG^  (CHLOROPHYCE^E)        207 

From  high-tide  mark  to  a  little  below  low-water  mark  Fucus 
and  Ascophyllum  (known  as  rockweeds)  often  form  dense  coat- 
ings upon  rocks.  At  low  tide  these  rockweeds  hang  loosely 

over  the  exposed  rocks.  Such  masses 
exhibit  the  dark  olive-green  color 
that  is  characteristic  of  the  group. 
190.  Sargassum  and  the  Sargasso 
seas.  Some  of  the  brown  algse  may 
become  detached  and  be  carried  hun- 
dreds or  even  thousands  of  miles 
from  their  original  growing  places. 
This  is  true  in  the  case  of  Sargassum, 
some  species  of  which  thrive  along 
the  shores  of  tropical  oceans.  In  the 
North  Atlantic  Ocean,  north  of  the 
Canary  Islands,  is  a  body  of  water 
known  as  the  Sargasso  Sea.  Its  entire 
area  is  more  or  less 
filled  with  floating  Sar- 
gassum and  other  forms 
of  plant  and  animal  life. 
In  other  similarly  quiet 
parts  of  the  seas  occur 
large  regions  filled  with 
floating  algse.  Sargas- 
sum,  as  is  also  true  of 
some  other  brown  algse, 
is  peculiarly  fitted  for 
floating  by  the  presence 
of  "  air  bladders,"  which 
are  swollen  regions  of 
the  leaf -like  expansions 
(Fig.  171).  In  mid- 
ocean  one  may  see  small  floating  masses  of  these  plants,  which 
have  been  carried  sometimes  hundreds  or  even  thousands  of 
miles  from  their  original  homes. 


FIG.  170.  The  stonewort  alga  (Chara) 

A,  a  slightly  magnified  piece  of  a  plant  showing 
the  general  appearance ;  B,  a  more  highly  mag- 
nified illustration  showing  the  oogonium  (o)  and 
the  antheridium  (a) ,  hy  means  of  which  repro- 
duction takes  place 


208 


PEACTICAL  BOTANY 


191.  The  kelps.  The  giant  kelps  belong  to  the  brown  algae, 
.and  are  represented  by  such  forms  as  Laminaria,  Postelsia, 
and  Macrocystis.  The  cylindrical  stem-like  growth  of  the 
Macrocystis  is  said  to  reach  a  length  of  from  800  to  900  feet, 
while  Laminaria,  or  "  devil' s-apron,"  grows  into  strap-like 

or  widely  spread, 
tough,  leathery 
expansions.  All 
of  these  forms 
have  heavy  root- 
like  holdfasts, 
which  furnish 
attachments  so 
strong  that  the 
plant  usually 
will  break  else- 
where before  it 
will  pull  away 
from  its  sup- 
port. The  great 
length  of  these 
plants  is  not  dis- 
posed vertically 
in  the  water,  but 
FIG.  171.  Rockweed  (Fucus)  the  strOngstem- 

A,  the  base  of  a  young  plant  showing  an  early  stage  in 
formation  of  the  holdfast,  which  attached  the  plant  to  a 
.piece  of  wood.  B,  tip  of  a  plant;  b,  air  bladders;  a,  spe- 
cialized regions  in  which  reproductive  organs  are  formed ; 
c,  new  leaf-like  growth  where  the  plant  had  been  broken. 


A  little  less  than  natural  size 


like  and  leaf- 
like  outgrowths 
trail  out  in  a 
semi-upright  po- 
sition. 

192.  Reproduction.  Vegetative  reproduction  in  the  brown 
algae  is  secured  by  the  breaking  apart  of  branches  from  old 
plants.  There  is  no  known  special  method  resulting  in  vege- 
tative reproduction,  as  in  Pleurococcus,  Nostoc,  etc. 

Some  members  of  the  group  {Ectocarpus  and  others)  are 
reproduced  by  zoospores  and  by  the  formation  of  zygospores 


THE  GREEN  ALG^l  (CHLOKOPHYCE^E)         209 


that  are  the  result  of  the  union  of  similar  motile  gametes, 
as  in  such  green  algae  as  Ulothrix  and  Cladophora.  Others, 
of  which  Fucus  is  a  representative,  reproduce  by  means  of 
oospores  that  are  formed  by  the  union  of  sperms  and  eggs.1 

193.  Uses  by  man.  At  one  time  the  world's  supply  of  iodine 
was  derived  from  the  brown  algse  ;  now  it  can  usually  be  pre- 
pared more  economically  by  chemical  means.    Soda  was  for- 
merly secured  from  these  plants,  but  chemical  processes  have 
driven  out  the  laborious  methods 

of  securing  that  substance  directly 
from  plants.  Gelatinous  foods  and 
a  sugar  known  as  mannite  are  se- 
cured from  some  species  of  brown 
algae.  In  some  coastal  portions  of 
this  country  the  farmers  collect 
and  carry  inland  great  quantities  of 
brown  algse  and  spread  them  over 
the  cultivated  land  as  a  fertilizer. 

194.  The    red    algae.     The    red 
algge  (Rhodophycece)  chiefly  inhabit 
deeper  water  than  do  the  brown 
algse.    The  class  is  almost  wholly 
confined  to  salt  water,  and  the  few 
that  do  live  in  fresh  water  do  not 

exhibit  well  the  color  characteristics  of  the  class.  One  com- 
mon fresh-water  genus  is  Batrachospermum  (Fig.  172). 

The  marine  forms  of  this  group  present  most  striking  shapes 
and  colors.  They  are  of  different  shades  of  red,  varying  from 
the  most  brilliant  to  those  that  are  dark  and  somber,  while 
some  are  a  deep  purple.  Chlorophyll  is  present,  but  often  is 
completely  obscured  by  the  other  colors.  Sometimes  all  the 
colors  are  obscured  by  deposits  of  calcareous  material  upon 
the  plants. 

1  If  desired  to  study  further  the  details  of  reproduction  of  the  brown 
algae,  see  Coulter,  Barnes,  and  Cowles,  College  Botany,  Vol.  I ;  also  Bergen 
and  Davis,  Principles  of  Botany. 


FIG.  172.  A  red  alga  (Batracho- 
spermum}, which  is  fairly  com- 
mon in  fresh  waters 

Slightly  magnified 


210 


PEACTICAL  BOTANY 


There  are  no  known  unicellular  red  algse.  Usually  the  plants 
are  quite  complex  and  present  expanded  leaf-like  structures 


FIG.  173.  A  red  alga  (Gigartina  spinosa) 
Attached  by  means  of  its  holdfast  to  a  small  stone 

(Fig.  173)  or  are  extensively  branched  (Fig.  174).  They  have 
basal  holdfasts,  which  in  general  resemble  those  usually  found 
in  the  brown  algse.  Red  algse  are,  as  a  rule,  smaller  and 


THE  GKEEN  ALG.E  (CHLOKOPHYCE^)         211 

more  delicate  than  the  brown  forms.1  There  are  often  many 
branches,  the  smallest  ones  becoming  quite  thread-like,  so 
that  the  entire  plant  looks  to  the  beginning  student  like  a 
sparsely  branched  stem  with  many  finely  divided  leaves.  In 
their  asexual  reproduction  the  red  algae  may  form  spores  in 
groups  of  four  (Fig.  175). 


FIG.  174.  A  red  alga  (Dasya) 

1  The  best  way  for  the  teacher  to  give  a  general  notion  of  brown  and  red 
algae  is  to  secure  card  mounts  or  bottled  material  for  class  demonstrations 
of  a  few  of  the  leading  types  in  each  group.  These  may  be  obtained  from 
the  Woods  Hole  Biological  Laboratory,  Woods  Hole,  Massachusetts,  and 
from  other  reliable  supply  houses.  Well-prepared  card  mounts  preserve  the 
natural  colors,  and  may  be  kept  indefinitely  for  laboratory  use. 


212 


PRACTICAL  BOTANY 


195.  Uses  of  red  algae.  Several  genera  of  the  red  algse  are 
used  as  food.     They  may  be  dried  and  thus  kept  for  long 

periods.  The  gelatinous  mate- 
rial that  is  secured  from  them 
forms  a  delicacy  much  de- 
sired by  some  people.  In  the 
North  Sea  and  elsewhere  in 
the  Atlantic  Ocean  occurs  a 
red  alga  known  as  "Irish 
moss,"  which  is  collected  in 
large  quantities  and  employed 
in  the  preparation  of  jelly,  to 
be  used  both  directly  as  food 
and  as  the  basis  for  the  prep- 
aration of  other  foods.  One  of 
these  gelatinous  products  of 
red  algae  is  agar-agar,  which  is 
extensively  used  as  a  growth 
medium  in  bacteriological 
work,  and  in  similar  work 
with  some  of  the  lower  fungi. 


FIG.  175.  The  asexual  reproduction 
of  a  red  alga  (Callithamniori) 

At  the  left  there  is  a  branch  upon  which 
is  a  sporangium.  Within  its  wall  its  di- 
vision into  four  spores  has  taken  place. 
At  the  right  these  four  asexual  spores 
have  escaped  from  the  sporangium. 
Much  magnified.  After  Thuret 


196.  Classification  of  the  algae : 

Thallophytes 
Algse 

Class  I.   Chlorophyceae  (the  green  algae) 

Leading  genera  used  as  illustrations,  —  Pleurococcus,  Spirogyra, 
Cladophora,    Ulothrix,    Draparnaldia,    Vaucheria,    Zygnema, 
CEdogonium,  Chara 
Class  II.   Phaeophyceae  (the  brown  algae) 

Leading  genera  used  as  illustrations, — Fucus,  Sargassum,  Lami- 

naria,  Ectocarpus 
Class  III.   Rhodophyceae  (the  red  algae) 

Leading  genera  used  as  illustrations,  —  Gigartina,  Dasya,  Calli- 
thamnion 


CHAPTER  XIV 
THE  ALG^E-FUNGI  (PHYCOMYCETES) 

197.  General  characteristics  of  the  fungi.  The  algae-fungi, 
as  the  name  suggests,  are  fungi  which  resemble  the  algae.    It 
was  noted  in  the  discussion  of  the  bacteria  that  the  fungi  are 
thallophytes  which  do  not  possess  chlorophyll.    Some  of  the 
fungi  are  so  much  like  the  algae  in  general  structure  that  if 
chlorophyll  were  added  to  them  they  might  easily  be  classi- 
fied together.    There  are  other  fungi  which  are  very  unlike 
the  algae. 

Absence  of  chlorophyll  suggests  the  absence  of  ability  to 
manufacture  foods  from  water  and  carbon  dioxide  (Sect.  17). 
"In  order  to  live,  fungi  must  secure  their  carbohydrate  food 
already  prepared  for  them,  and  the  first  great  question  that 
arises  relates  to  the  ways  in  which  non-chlorophyll-bearing 
plants  secure  their  food. 

198.  The  dependent  habit  of  living.  The  dependent  habit  is 
characteristic  of  the  fungi,  though  there  are  many  dependent 
plants  that  do  not  belong  to  the  fungi.    Dependency  may 
appear  in  any  one  of  several  forms.    Such  fungi  as  toadstools, 
mushrooms,  and  puffballs  live  upon  decaying  plant  and  ani- 
mal material,  —  old  leaves,  logs,  stumps,  manure  heaps,  etc.,— 
and  when  so  living  are  called  saprophytes.    Sometimes  depend- 
ent plants  live  upon  living  plants  or  animals,  as  in  the  case  of 
tree-destroying  fungi,  wheat  rust,  and  some  of  the  bacteria  of 
the  human  body.    These,  as  we  have  seen,  are  called  parasites, 
and  the  organism  which  furnishes  the  food  material  is  the  host. 
Two  living  organisms,  plant  or  animal,  may  live  together  in 
such  a  way  that  each  benefits  from  the  presence  of  the  other, 
•and  sometimes  these  are  called  mutualists,  meaning  "  mutually 
helpful,"  and  sometimes  they  are  called  helotists,  meaning  that 

213 


214  PRACTICAL  BOTANY 

one  organism  is  held  by  the  other  in  a  condition  of  slavery. 
In  case  of  some  dependent  plants  it  is  not  easy  to  determine 
the  nature  of  their  dependency.1 

199.  Bread  mold  (Rhizopus  nigricans).    If  a  piece  of  slightly 
moistened  bread  is  placed  in  a  glass  jar  or  covered  in  a  dish 
for  a  few  days,  an  abundant  supply  of  mold  soon  appears  upon 
it.    There  may  even  be  several  kinds  of  molds  developed  upon 
the  bread  under  such  conditions  within  a  very  few  days.    The 
common  bread  mold,  or  black  mold,  is  the  one  which  usually 
appears.    It  grows  about  our  homes  in  great  abundance,  soon 
appearing  when  bread,  fruits,  and  other  favorable  nutrient 
substances  are  left  exposed.    When  young  the  mold  is  white, 
only  assuming  its  blackish  appearance  when  spores  are  formed. 

200.  Bread  mold :  vegetative  structures.  A  mass  of  growing 
bread  mold  is  composed  of  many  white  threads  greatly  entangled 
one  with  another.    This  entanglement  is  due  to  the  forward 
growth  of  the  many  free  ends  of  these  threads.  Each  thread  is 
called  a  hypha  (meaning  "a  single  web"),  and  the  whole  net- 
work of  hyphce  is  the  mycelium,  or  fungus  mass.  The  mycelium 
is  the  interwoven  network  of  which  one  hypha  is  a  single  thread. 

Careful  examination  also  shows  that  some  of  the  hyphse 
have  grown  down  into  the  nutritive  substratum  (supporting 
substance),  and  if  one  could  see  through  the  bread  after  mold 
has  grown  on  it  for  a  few  days,  much  of  the  mycelium  would 
be  seen  within  the  bread.  Branching  downward  from  some  of 
the  superficial  hyphas  are  special  root-like  hyphse  (rhizoids) 
(Fig.  176),  which  descend  and  spread  out  within  the  nutrient 
material.  At  such  places  upright  hyphae  also  are  formed. 
From  these  areas  long  runner-like  branches  (stolons)  may 
extend  over  the  surface  a  little  way.  From  the  stolons  a  new 
set  of  rhizoids  and  upright  hyphae  may  be  formed.  This 
method  of  vegetative  extension  gave  rise  to  a  much-used  name, 
Mucor  stolonifer,  meaning  "  the  stolon-bearing  mold." 

1  Dependent  plants  are  treated  more  fully  in  a  separate  chapter,  but  plant 
dependency  necessarily  receives  attention  throughout  ttus,  discussion  of  the 
fungi. 


THE  ALG^-FUNGI  (PHYCOMYCETES)          215 

Under  magnification  hyphse  of  bread  mold  are  seen  to  con- 
sist of  heavy  tubular  cell  walls  in  which  the  granular  proto- 
plasm is  not  separated  by  trans- 
verse walls,  as  it  is  in  most  of 
the  algae.  If  the  nuclei  could 
be  seen,  which  is  not  possible 
in  unstained  material,  many  of 
them  would  be  found  within 
the  tubular  hyphal  wall.  This 
plant,  therefore,  is  a  coenocyte, 
like  the  green  alga  VaucTieria 
(Sect.  183).  If  Rhizopus  pos- 
sessed chlorophyll,  it  would  re- 
semble the  vegetative  structure 
of  Vaucheria. 


FIG.  176.  Black  mold 

Below  is  a  slightly  magnified  illustration  of  plants,  one  of  which  has  given  rise 
to  the  other  by  means  of  a  runner,  or  stolon.  Descending  are  the  rhizoids  and  as- 
cending are  the  aerial  branches,  upon  the  tips  of  which  spores  are  borne  within 
sporangia.  Above  and  at  the  right  a  more  highly  magnified  sporangium  is  shown. 
Its  wall  (w)  incloses  many  spores  (s),  through  which  may  be  seen  the  columella 
(c),  which  is  the  swollen  tip  of  the  stalk  upon  which  the  sporangium  is  borne. 
This  wall  may  be  broken  away,  so  as  to  leave  some  of  the  spores  lying  upon  the 
columella,  as  is  seen  in  two  cases  of  the  plants  shown  below 

201.  Bread  mold:  nutrition.  Bread  mold  lives  upon  and 
within  its  nutrient  substance  and  absorbs  food  material  directly 
from  it.  Parts  that  are  in  contact  with  the  substratum  do  the 


216  PRACTICAL  BOTANY 

work  of  food  absorption.  Food  is  carried  through  the  tubular 
cells  to  the  parts  of  the  mycelium  that  are  above  the  food 
material. 

202.  Bread  mold :  effect  upon  the  substratum.  If  a  piece  of 
bread  upon  which  bread  mold  is  growing  vigorously  be  -kept 
moist,  the  mold  will  not,  usually,  continue  to  grow' until  the 
bread  is  completely  consumed.    Either  because  of  having  se- 
cured all  the  food  it  can  extract  from  the  bread,  because  of 
having  secreted  substances  that  prevent  its  further  growth,  or 
because  of  being  unable  to  hold  its  own  with  other  organisms 
(molds  and  bacteria),  the  bread  mold  after  a  time  ceases  to 
grow.   Other  molds  and  bacteria  may  appear,  one  kind  follow- 
ing another  for  weeks,  until  the  decay  of  the  bread  is  almost 
or  quite  complete.    If  kept  tightly  sealed,  however,  growth 
stops  before  all  the  food  material  is  used.    Molds  often  grow 
for  a  time  in  jars  of  fruit,  forming  upon  the  top  of  the  fruit 
a  coating  which  remains  until  the  jar  is  opened.    If  this  coat- 
ing is  removed  and  a  fresh  supply  of  air  is  admitted,  a  new 
growth  soon  appears. 

203.  Bread  mold:  asexual  reproduction.  In  addition  to  vege- 
tative reproduction  by  means  of  stolons,  this  mold  also  repro- 
duces itself  both  asexually  and  sexually.    There  arise  from  the 
main  body  of  the  mycelium  upright  hyphse,  upon  the  ends  of 
which  sporangia  are  produced  (Fig.  176).    The  upright  stalks 
are  called  sporangiopliores  (meaning  "  sporangia  bearers").    In 
the  development  of  the  sporangium,  first  a  transverse  wall  cuts 
off  a  small  tip  of  the  upright  stalk.  This  tip  cell  grows  rapidly 
until  it  has  become  a  large  spherical  body.    Meanwhile  the 
transverse  wall  has  extended  into  the  spherical  sporangium, 
thus  producing  a  little  column  (the  cdumella)  upon  which  the 
sporangium  contents  rest.    The  protoplasm  of  the  sporangium 
divides  into  many  small  spores,  which,  when  the  sporangium 
wall  breaks,  are  scattered  widely  into  the  air.    The  musty  odor 
which  is  detected  when  we  smell  mold  may  be  due  to  the 
presence  of  large  numbers  of  these  spores,  or  to  gases  thatr 
have  been  produced  within  the  nutrient  material. 


THE  ALG^-FUNGI  (PHYCOMYCETES)          217: 

If  bread  that  has  not  been  exposed  to  the  air  is  cut  in  a 
room  in  which  the  air  is  quiet,  and  if  one  piece  'is  covered 
directly  in  a  glass  dish,  another  similarly  covered  after  five 
minutes'  exposure  to  the  air  of  the  room,  and  another  after 
five  minutes'  exposure  on  the  outside  window  sill,  an  interest- 
ing test  of  the  abundance  of  spores  in  the  atmosphere  will  be 
afforded.  One  class  of  students, 
in  performing  this  experiment, 
.secured  the  development  of  mold 
upon  all  three  pieces  of  bread, 
having  in  all  five  kinds  of  mold. 

204.  Bread  mold :  sexual  re- 
production.   Bread  mold  rarely 
reproduces  itself  by  sexual  proc- 
esses, but  does  so  under  some 
circumstances.    The  tips  of  hy- 
phse  approach  one  another,  and 
end  cells  are  formed  by  means 
of  transverse  walls.   These  end 
cells  gradually  unite  to  produce 
a  spore,  and  a  heavy  dark  wall 
is  formed  about  it.    Since  this 
spore  is  produced  by  the  union 
of  similar  cells  it  is  called  a  zy- 
gospore.   It  is  a  well-protected 
spore,  and  seems  fitted  for  en- 
during great  extremes  in  physical  conditions.-    The  germi- 
nation of  the  zygospore  of  Rhizopus  nigricans  is  an  occurrence 
that  is  difficult  to  demonstrate  in  the  laboratory,  thougK  it 
and  closely  related  molds  (Mucor  mucedo  and  Sporodinia)  form 
zygospores  that  have  been  seen  to  germinate  and  thus  repro- 
duce the  mold  plants.   The  similarity  between  the  formation 
of  zygospores  in  molds  and  in  Spirogyra  is  worthy  of  note. 

205.  Water  mold  (Saprolegnid).   Although  there  are  several 
kinds  of  water  molds,  this  is  the  most  common  one.    It  lives 
in  the  water,  upon  dead  insects,  fish,   and   other  animals. 


FIG.  177.  Water  mold  growing  on 
the  body  of  a  wasp 

The  fungus  has  grown  upon  the  host 

until  an  extensive  white  fluffy  mass 

has  been  formed 


218 


PRACTICAL  BOTANY 


Sometimes  living  fish  that  are  confined  in  close  quarters  become 
infested  with  this  mold  and  die.  In  such  cases  the  mold  is 
first  a  parasite,  but  upon  the  death  of  its  host  it  becomes  a 
saprophyte.  In  late  summer  and  early  autumn,  flies  and  other 
insects  often  become  infected  with  water  molds  and  related 
fungi  (as  Entomopktliora).  If  these  insects,  when  found  lying 
on  the  floors  and  window  sills,  are  placed 
in  a  dish  of  water,  the  mold  sometimes 
grows  rapidly,  soon  producing  a  "collar" 
of  fluffy  hyphse  about  the  thorax  of  the 
insect,  and  may  cover  the  entire  body 
(Fig.  177). 

206.  Water  mold:  vegetative  structures 
and  nutrition.    The  mycelium  of  Sapro- 
legnia  branches  and  extends  itself  through- 
out the  tissues  of  its  supporting  material. 
As  in  Mucor  and  Vaucheria,  the  plant  is 
a  coenocyte.    It  absorbs  its  food  material 
directly,  and  when  the  supply  of  food  is 
abundant  it  may  grow  with  striking  ra- 
pidity.   This  plant  is  effective  in  bring- 
ing about  decay  of  dead  animal  bodies  in 
the  water. 

207.  Water  mold:  asexual  reproduction. 
At    times   the    numerous    hyphse    which 
extend  from  the  nourishing  material  may 
form  transverse  walls,  which  separate  large 

swollen  tip  segments  from  the  bases  of  the  hyphse.  Within  each 
tip  segment  many  zoospores  form  (Fig.  178).  These  escape 
into  the  water  in  very  large  numbers  and  swim  about  quite 
actively.  Upon  coming  in  contact  with  favorable  nutriment  the 
cilia  are  withdrawn  and  the  zoospore  germinates  into  a  new 
hypha,  which  by  growth  may  produce  a  new  mycelium. 

208.  Water  mold :  sexual  reproduction.  From  the  tips  of 
short  hyphae  large  spherical  cells  (oogonia)  are  formed,  in 
each  of  which  one  to  many  eggs  are  produced.  In  some 


FIG.  178.  A  water  mold 
bearing  a  sporangium 
(s),  from  which  zoo- 
spores  (z)  are  escaping 

After  Schenck 


THE  ALGLE-FUNGI  (PHYCOMYCETES)          219 

species  groups  of  oogonia  are  formed  upon  a  single  hypha. 
Antheridial  branches  come  in  contact  with  the  oogonia  (Fig. 
170).  A  tube  grows  from  the  antheridium  and  pierces  the 
wall  of  the  oogonium.  Sperms  from  the  antheridium  escape 
and  fertilize  the  eggs,  thus  forming  oospores  which  can  repro- 
duce the  plant.  In  some  cases  when  Saprolegnia  eggs  are 
not  fertilized  they  develop 
heavy  walls,  and  after- 
wards germinate  as  if  they 
had  been  fertilized.  Such 
development  of  eggs  into 
oospores  without  fertiliza- 
tion is  known  as  partheno- 
genesis. It  is  a  method  of 
reproduction  that  is  met 
with  in  some  other  plants 
and  in  some  animals. 

209.  The  grape  downy 
mildew  (Plasmopara  viti- 
cola).  There  are  numerous 
so-called  downy  mildews ; 
the  one  here  used  as  a  type 
frequently  appears  upon 
the  under  surface  of  leaves 
of  the  grape.  In  the  Cen- 
tral States,  which  region  is  Some  of  the  hyphse  bear  oogonfa  (o)  and  an- 
,  .  ,  .,  .  .  ,  theridia  (a),  and  within  the  oogonia  are  the 

supposed  to  be  the  original  eggs  (e).  After  Kiebs 

home  of  this  parasite,  it  has 

been  an  injurious  pest  for  many  years.  Its  downy  white  growth 
upon  the  surface  of  the  leaves  (Fig.  180)  is  its  most  con- 
spicuous distinguishing  characteristic,  but  it  also  often  grows 
upon  green  shoots  and  fruit.  When  conditions  are  thoroughly 
favorable  (proper  soil,  moisture,  and  temperature)  for  the 
growth  of  grapevines,  the  parasite  when  present  may  do  little 
damage.  At  other  times  it  may  all  but  destroy  the  crop  and 
greatly  reduce  the  vigor  of  the  host  plant. 


FIG.  179.  Sexual  reproduction  of  a  water 
mold 


220  PRACTICAL  BOTANY 

210.  Grape  mildew :  vegetative  structures  and  nutrition. 
The  downy  patches  that  appear  upon  the  leaves  are  merely 
the  superficial  parts  of  the  parasite,  since  within  the  leaf  the 


FIG.  180.  A  leaf  of  the  grape,  upon  which  may  be  seen  the  white,  fluffy  patches 

of  grape  mildew 
Photograph  by  H.  H.  Whetzel 

mycelial  hyphse  have  grown  for  some  time  before  the  downy 
patches  are  produced.  These  ccenocytic  hyphse  grow  between 
the  cells  and  send  into  the  interior  of  the  cells  short  branches 


THE  ALGLE-FUHG1  (PHYCOMYCETES)          221 


(hamtoria),  which  absorb  food  directly  from  the  cell  contents 
of  the  host  (Fig.  181,  -B).  When  the  mildew  has  thus  grown 
within  the  leaf 
for  a  time,  it 
sends  through 
the  stomata 
on  the  under 
surface  numer- 
ous branches 
which  consti- 
tute the  super- 
ficial downy 
patches  char- 
acteristic of 
the  parasite. 

211.  Grape  mildew :  asex- 
ual reproduction.  Some  of 
the  aerial  hyphse  branch  and 
upon  tips  of  these  branches 
produce  spore-like  bodies, 
the  conidia  (Fig.  181,  A). 
These  conidia  fall  from  the 
conidiophores  (conidia  bear- 
ers), and  when  favorable 
moisture  (dew,  rain,  etc.) 
is  present  they  germinate. 
Instead  of  producing  new 
hyphse  they  usually  act  as 
sporangia  and  produce  ZOO- 


FIG.  181.  Grape  mildew  (Plasmopara) 


From  the  mycelium  within  the  cells  of 
the  grape  leaf  haustoria  (Z?)  are  formed. 
Upright  hyphse  (A)  bear  conidia.  These 
conidia  divide,  as  at  D,  and  form  zoo- 
spores  (E).  Within  the  leaf  oospores  (C) 
are  formed.  After  Duggar 


spores  (Fig.  181,  D  and  E). 

The    z  oospores    may  swim 

about  for  fifteen  or  twenty 

minutes,  and  then  lose  their 

cilia  and  begin  to  produce  new  hyphae.  If  favorably  located,  the 

new  hyphse  may  find  entrance  to  a  leaf  through  its  stomata 

and  begin  anew  the  growth  therein. 


222  PRACTICAL  BOTANY 

212.  Grape  mildew:  sexual  reproduction.   In  the  interior  of 
the  leaf  short  hyphal  branches  develop  into  obgonia  and  an- 
theridia  (Fig.  181,  (7).  Each  obgonium  develops  an  egg,  which, 
when  fertilized  by  one  of  the  many  sperms  from  the  anther- 
.idium,  becomes  an  obspore.    This  obspore  has  a  heavy  wall 
and  also  is  within  the  tissues  of  the  leaf,  so  that  apparently 
it  is  well  fitted  to  endure  severe  winter  conditions.    Upon  the 
decay  of  the  leaf  the  obspores  are  set  free.    They  probably  ger- 
minate to  produce  new  plants,  but  "  much  work  needs  to  be 
done  in  the  way  of  determining  to  what  extent  the  obspores 
are  necessary  in  the  annual  propagation  of  this  species."1 

213.  Grape  mildew:  preventive  measures.  Usually  it  is  pos- 
sible to  control  the  growth  of  this  parasite  so  that  serious  damage 
is  prevented.  In  1881  the  Frenchman  Millardet  began  experi- 
menting with  the  Bordeaux  mixture  2  as  a  method  of  treating 
grape  mildew.    His  experiments  resulted  in  a  chemical  mix- 
ture which,  when  properly  used  as  a  spray,  will  obviate  most  of 
the  ill  effects  of  grape  mildew.    The  same  mixture  has  been 
found  of  great  value  in  treating  many  other  plant  diseases, 
and  almost  all  the  state  agricultural  experiment  stations  issue 
special  directions  concerning  local  uses  of  this  mixture. 

214.  Potato  blight  (Phytophthora  infestans).  This  parasite  is 
a  near  relative  of  grape  mildew.    Its  vegetative  characteristics 
closely  resemble  those  just  described.    Its  asexual  reproduc- 
tion by  conidiospores  and  the  consequent  z  obspores  gives  it 
very  ready  and  wide  distribution.    The  parasite  may  infest 
leaf,  stem,  or  tuber  of  the  potato,  and  is  one  of  the  several 
fungous  diseases  that  have  proved  very  destructive  of  potato 
crops.    It  may  be  held  in  check  by  proper  spraying  (Fig.  349) 
with  the  Bordeaux  mixture.3 

1  Duggar,  B.  M.,  Fungous  Diseases  of  Plants.    Ginn  and  Company,  Bos- 
ton, 1909. 

2  The  preparation  as  most  commonly  used  consists  of  materials  mixed  in 
the  following  proportions  :  copper  sulphate,  5  pounds ;  stone  lime,  6  pounds  ; 
water,  50  gallons.   Other  proportions  are  often  used. 

8  "Potato  Spraying  Experiments  in  1906,"  Bulletin  279,  N.Y.  Agr.  Exp.  Sta. ; 
"Certain  Potato  Diseases  and  their  Remedies,"  Bulletin  7£,Vt.  Agr.  Exp.  Sta. 


THE  ALG.E-FUNGI  (PHYCOMYCETES)          223 

215.  Other  phycomycetes.  Of  the  forms  that  have  here  been 
discussed,  —  Rhizopus,  Saprolegnia,  and  Plasmopara, —  each 
represents  an  important  subdivision  of  the  phycomycete  class 
of  fungi.    There  are  many  molds  closely  related  to  Rhizopus, 
and  some  of  them  usually  appear  wherever  there  is  decaying 
organic  matter.    Several  kinds  of  water  molds  are  known, 
and  other  parasitic  forms  which  resemble  Saprolegnia  are  the 
cranberry-gall  fungus  (Synchytrium  Vacdm),  which  attacks 
the  stem,  leaves,  flowers,  and  fruit  of  the  cranberry  plant; 
the  "  damping-off  "  fungus  (Pythium  DeBaryanum),  which,  in 
plant-house  seed  beds  and  sometimes  in  open  fields,  kills  seed- 
ling plants  by  attacking  their  cells  at  or  near  the  soil,  thus 
causing  them  to  wilt ;  the  brown  rot  of  the  lemon  and  other 
citrous  fruits  (Pythiacystis  citrophthora),  which  is  especially 
injurious  in  California  and  is  often  a  forerunner  of  the  blue 
mold  (JPmicillium).    Important  plant  parasites  which  in  struc- 
ture and  habit  resemble  the  grape  mildew  and  potato  blight 
are  the  white  or  downy  mildew  (  Cystopus  candidus,  sometimes 
called  Albugo  Candida)  of  plants  of  the  mustard  family  ( Oru- 
ciferce),  as  shepherd's-purse,  the  common  radish,  horse-radish, 
cress,  mustard,  and  turnip ;  also  another  white  mildew  (Pero- 
nospora  parasitica)  which  infests  many  members  of  the  mus- 
tard family,  including  most  of  those  mentioned  for  Cystopus, 
as  well  as  others  ;  downy  mildew  (Plasmopara  cubensis)  of  the 
cucumber,  pumpkin,  and  watermelon  ;  onion  mildew  (Peronos- 
pora  Schleideni)  ;  downy  mildew  of  lettuce  (Bremia  Lactucce) 
and  downy  mildew  of  lima  beans  (PhytopTithora  Phaseoli). 

216.  Summary  of  phycomycetes.  In  structure  and  methods 
of  reproduction  this  group  resembles  some  of  the  green  algae. 
The  frequently  occurring  ccenocytic  body  suggests  Vaucheria 
and  its  relatives    among  the   green  algse.    In  reproduction 
zobspores,  zygospores,  and  ob'spores  are  formed,  and  the  spe- 
cialized sex  organs,  oogonium  and  antheridium,  are  present. 
In  some  of  the  phycomycetes  specialized  asexual  structures, 
the  conidia,  are  formed,  and  these  germinate,  usually  producing 
one  or  more  zoospores.    Evidently  these  conidia  are  sporangia 


224  PRACTICAL  BOTANY 

which  fall  from  the  parent  plant  before  the  spores  that  de- 
velop within  them  are  set  free.  A  careful  review  of  type 
plants  used  in  the  study  of  green  algae  and  phycomycetes 
will  show  striking  similarity  in  reproductive  processes. 

The  saprophytic  and  parasitic  habits  of  living  of  this  group 
give  them  very  great  economic  significance.  Agriculture,  hor- 
ticulture, gardening,  fish  industries,  and  water  supplies  are 
seriously  affected  by  members  of  the  group. 

217.  The  groups  of  fungi.  The  classification  of  dependent 
plants  into  saprophytes,  parasites,  mutualists,  and  helotists  is 


FIG.  182.  Slime  mold  (Fuligo)  growing  from  a  decaying  board 

Two  masses  have  exuded  from  the  crevices  of  the  board  and  are  rounded  into 
position  for  forming  spores.   Natural  size 

based  entirely  upon  the  ways  in  which  plants  live.  Fungi  are 
also  classified  upon  the  basis  of  their  structure,  and  this  classi- 
fication is  the  one  generally  used  in  speaking  of  them.1  The 
leading  groups  or  classes  are  the  phycomycetes,  ascomycetes, 
lichens,  and  basidiomycetes.  The  schizomycetes  (bacteria)  are 
sometimes  treated  in  this  connection,  but  by  reason  of  sim- 
ilarity of  structure  and  methods  of  reproduction  they  and  the 
blue-green  algae  are  now  discussed  together  (Chapters  XI 
and  XII).  The  last  part  of  the  name  of  each  class  (mycetes) 
means  "fungi,"  and  the  first  part  refers  to  a  distinguishing 

1  The  simplest  acceptable  classification  of  fungi  has  been  adopted.  Certain 
technical  groupings  that  are  quite  proper  in  a  more  advanced  treatise  are 
omitted  from  this  elementary  statement. 


THE  ALG.E-FUNGI  (PHYCOMYCETES)          225 

characteristic  of  the  class.  Thus  phycomycetes  literally  means 
"  seaweed  fungi,"  and  we  call  them  algae-fungi ;  ascomycetes 
means  "sac  fungi,"  since  some  of  the  spores  are  formed  in  a 
peculiar  sac  ;  and  the  basidiomycetes  are  the  "  stalk  fungi,"  or 
"  club  fungi,"  since  some  of  the  spores  are  borne  upon  a  stalk 
or  club-like  base.  In  each  of  these  classes  many  kinds  of  fungi 
are  found,  but  only  a  few  kinds  in  each  class  can  be  consid- 
ered in  an  elementary  treatment.1  The  lichens  are  peculiar 
plants,  which  are  treated  in  this  connection  merely  for  lack  of 
better  classification  for  them,  as  will  appear  later. 

218.  Classification: 

Thallophytes 
Algae 
Fungi 

Class  I.  Phycomycetes.  Leading  genera  used  as  illustrations,  — 
Rhizopus  (bread  mold),  Saprolegnia  (water  mold),  Plasmopara 
(grape  downy  mildew),  Phytophthora  (potato  blight),  Cystopus, 
and  others 

Class    II.   Ascomycetes 
Class  III.   Lichens 
Class  IV.   Basidiomycetes 

1  The  "  slime  molds,"  or  myxomycetes,  are  usually  classed  with  the  fungi, 
though  some  students  regard  them  as  animals.  They  often  appear  as  ge- 
latinous, sticky,  yellow,  brown,  or  brightly  colored  masses  exuding  from 
crevices  in  old  stumps,  logs,  old  board  walks,  upon  decaying  leaves,  and 
sometimes  upon  very  rich  soil  (Fig.  182).  At  other  times  these  masses  pro- 
duce stalks,  globules,  or  one  or  a  few  rounded  masses.  These  are  the  spore- 
producing  structures.  So  different  are  these  two  stages  —  one  motile  like 
some  of  the  lower  animals,  the  other  forming  spores  like  some  plants  —  that 
students  formerly  thought  the  two  stages  were  different  organisms,  of  which 
one  was  animal,  the  other  plant. 


CHAPTER  XV 

THE  SAC  FUNGI  (ASCOMYCETES)  ;   THE  LICHENS; 
THE  BASIDIUM  FUNGI  (BASIDIOMYCETES) 

THE  SAC  FUNGI  (ASCOMYCETES) 

219.  General  characteristics.    More  of  the  fungi  belong  to 
this  class  than  to  any  other,  and  since  most  of  the  ascomycetes 
are  parasitic,  it  is  evident  that  the  class  is  one  of  great  im- 
portance.   There  is  wide  variation  in  form  and  structure  in 
this  group.   The  mycelium  of  the  parasitic  forms  grows  mainly 
upon  instead  of  within  the  host,  and  sends  into  it  short  haus- 
toria  which  absorb  food  material.  The  hyphse  of  the  mycelium 
are  divided  into  many  cells,  and  branch  extensively.    Many 
of   the   known  structures    are    difficult  to  understand,   and 
many  of  the  facts  are  not  known  regarding  the  life  cycles  of 
some  of  the  plants  which  belong  in  this  class.    In  a  general 
way,  the  fungi  of  this  class  are  subdivided  into  two  groups,  — 
those  which  have  their  spore-forming  sacs  opening  into  cup- 
like  structures,  and  those  which  have  the  spore  sacs  inclosed, 
or  almost  inclosed,  in  heavy-walled  and  more  or  less  spheri- 
cal cases.    Common  illustrations  of  the  class  are  the  mildews 
which  grow  upon  leaves  of  the  plantain,  smartweed,  and  lilac, 
the  cup  fungi,  the  morel,  and  yeasts.    Of  the  many  represent- 
atives, but  a  few  types  will  be  used  to  give  some  general 
notions  of  the  structure  and  importance  of  the  class. 

220.  Peziza  and  Sclerotinia.  In  damp  soil,  attached  to  decay- 
ing sticks  or  roots,  may  be  found  the  pink  or  reddish  cup  fungus, 
Peziza.    Peziza  plants  sometimes  appear  singly  and  sometimes 
in  clusters  or  rows,  and  in  color  some  of  them  are  very  striking. 

Growing  from  old  plums  and  peaches  which  have  shriveled 
and  dried  (become  mummified),  sometimes  there  are  found 
similar  though  brownish  cups,  which  contain  the  reproductive 

220 


THE  SAC  FUNGI  (ASCOMYCETES) 


227 


organs  of  another  ascomycete,  Sderotinia  (Fig.  183).  In  case 
of  both  Peziza  and  Sderotinia,  the  cups  are  external  indica- 
tions of  a  much  larger  internal  growth  of  the  fungus.  In 
Sderotinia^  commonly  called  the  brown  rot  of  the  stone  fruits 
(peach,  plum,  apricot,  cherry),  the  infection  of  the  host  long 
precedes  the  production  of  cups.  Mycelial  hyphse  penetrate  the 
fruit  or  the  flower  and  grow  extensively  in  it,  often  extending 
to  the  twig.  After  a  period  of  such  growth  there  appear  upon 
the  surface  of  the  fruit,  which  is  now  shriveling  or  decaying, 


FIG.  183.  Brown  rot  (Sderotinia)  growing  upon  old  plums 

At  the  right  are  some  of  the  fruiting  cups;  in  the  middle  is  a  greatly  magnified 

portion  of  the  cup,  showing  the  spore-bearing  areas ;  and  at  the  left  is  one  of  the 

spore-bearing  threads  still  more  magnified.   After  Duggar 

many  tufts  of  light-brown  hyphse.  Among  these  tufts  are 
conidiophores,  upon  which  conidia  are  produced.  These  con- 
idia  are  scattered  by  wind,  by  contact  with  insects,  etc.,  and, 
alighting  upon  favorable  growing  places,  produce  new  myce- 
lial  growths.  It  is  thought  possible  that  these  conidial  spores 
may  persist  throughout  the  winter.  Infected  fruits  may  be- 
come dried  and  shriveled,  and  hang  upon  the  tree  or  fall  to 
the  ground.  When  favorable  growing  conditions  return  in  the 
next  season,  or  even  in  a  later  season,  the  brown  cups  are  pro- 
duced from  the  mass  of  mycelium  in  the  old  fruit.  These  cups 
are  composed  of  many  hyphse  closely  pressed  together.  In  the 
tips  of  some  of  these  hyphse  in  the  bottom  of  the  cups  the  spores 


228. 


PRACTICAL  BOTANY 


are  formed  (Fig.  183).  The  wall  of  a  spore-containing  hypha 
is  the  sac  or  ascus,  and  the  spores  which  are  formed  therein 
are  the  ascospores,  or  sac  spores.  These  spores,  when  favorably 
placed,  again  produce  the  mycelium  of  the  parasite.  This  repre- 
sents the  chief  method  of  spring  and  early  summer  infection 
of  fruits  with  the  brown  rot. 

221.  Destructiveness  of  Sclerotinia.  All  kinds  of  stone  fruits 
seem  to  be  susceptible  to  attacks  of  this  disease.    It  is  said1: 

"  It  would  appear  that  among 
peaches  the  sorts  densely 
covered  with  hairs  or  down, 
such  as  Alexander,  Hill's 
Chili,  and  Triumph,  are  usu- 
ally susceptible.  Among  the 
more  resistant  sorts  are  to 
be  found  the  Carmen,  Early 
Crawford,  Elberta,  Chinese 
Cling,  and  some  others. 
Among  the  plums  the  Jap- 
anese varieties  suffer  gen- 
erally in  most  sections  of 
the  country.  The  American 
group  of  plums  is  also  sus- 


FIG. 184.  A  group  of  "morel"  mush- 
.  rooms  (Morchella) 


Note  the  depressions  in  the  surface,  in 

which  the  sacs  and  ascospores  are  formed.  , 

Three  fourths  natural  size  ceptible,  and  apparently  more 

susceptible  at  the  South  than 

farther  north.  The  Wild  Goose  and  Marietta  plums  are  much 
less  affected  in  all  regions.  The  native  cherries  are  more  resist- 
ant than  such  as  the  Montmorency."  The  total  amount  of  the 
damage  is  enormous.  In  1887  Maryland  and  Delaware  were 
reported  to  have  had  a  peach-crop  shortage,  from  this  cause,  of 
800,000  baskets  of  fruit.  In  1900  Georgia  had  an  estimated 
loss  of  40  per  cent  of  the  peach  crop,  or  a  money  loss  of  be- 
tween $500,000  and  S700,000.2  The  disease  may  be  checked 

1  Duggar,  Fungous  Diseases  of  Plants.    Ginn  and  Company,  Boston,  1910. 

2  "The  Brown  Rot  of  Peaches,  Plums,  and  Other  Fruits,"  Bulletin  50, 
Georgia  Agr.  Exp.  Sta.,  1900. 


THE  SAC  FUNGI  (ASCOMYCETES)  229 

by  destroying  the  infected  fruits  and  twigs.  Spores  are  so  gen- 
erally distributed  that  spraying  is  also  necessary.  Different 
sprays  have  been  used,  but  with  such  varying  success  that 
the  advice  of  local  experiment  stations  should  be  sought  for 
the  special  needs  in  each  state. 

222.  The  morel  (Morchelld).  Another  representative  of  the 
open-fruiting  ascomycetes  is  that  commonly  called  the  "morel 
mushroom"  (Fig.  184).  Its  mycelium  grows  in  earth  that  is 


FIG.  185.  Leaves  of  lilac  upon  which  lilac  mildew  appears  in  whitish  patches. 
Also  the  small  dark  reproductive  bodies  are  shown 

very  rich  with  decaying  organic  matter.  It  is  usually  found  in 
woods  among  the  leaves  and  about  old  logs  and  stumps.  The 
fruiting  body,  the  mushroom,  is  the  only  part  usually  noticed, 
and  under  favorable  conditions  of  moisture  and  temperature  it 
develops  in  a  very  short  time,  growing  at  the  expense  of  food 
material  that  is  gathered  by  the  underground  saprophytic  my- 
celium. In  the  deep,  wrinkle-bordered  pits  of  the  mushroom 
are  the  ascus-bearing  hyphse.  The  ascospores  form  in  great 
numbers  and  are  so  light  that  they  may  be  widely  distributed. 
223.  The  powdery  mildews:  lilac  mildew  (Microsph&ra alni). 
Good  illustrations  of  the  inclosed-fruited  ascomycetes  are  had 
in  the  powdery  mildews.  They  are  frequently  found  upon  the 
surfaces  of  leaves  of  lilac  (Fig.  185),  and  related  mildews  are 


230 


PRACTICAL  BOTANY 


found  upon  the  willow,  aak,  some  of  the  smartweeds,  and 
upon  many  other  plants.  The  powdery  mycelium  lives  upon 
the  surfaces  of  the  leaves.  Haustoria,  by  means  of  which 
nutrient  material  is  extracted  from  the  host,  are  sent  into  the 
leaf  from  the  superficial  hyphse.  The  fungus  is  therefore  a 
superficial  parasite. 

At  times  upright  hyphse   form   transverse  walls,   cutting 
from  their  tips  rows  of  small  cells,  the  conidia.    The  powdery 

appearance  of  the  mildews 
is  due  largely  to  the  pres- 
ence of  large  numbers  of 
these  conidia.  The  co- 
nidia, if  favorably  placed, 
are  the  means  of  produc- 
ing new  growths  of  the 
ascocarp  mildew.  Another  complex 

method  of  reproduction 
results  in  forming  asco- 
spores.  Two  superficial 
hyphse  unite  their  tips, 
and  fusion  of  the  nuclei 
of  these  tip  cells  takes 
place.  Then  there  grows, 
as  a  result  of  this  fusion, 
a  relatively  large,  heavy- 
walled  body,  the  asco- 
carp,  so  called  because  it  is  the  hard-walled  body  which  con- 
tains the  asci  and  ascospores.  Within  the  developing  asco- 
carp, division  of  the  tissue  finally  results  in  forming  several 
asci,  in  each  of  which  there  are  four  to  eight  ascospores 
(Fig.  186).  In  late  summer  the  ascocarps  may,  without  mag- 
nification, be  seen  as  small  black  bodies  upon  the  surface  of 
lilac  leaves.  From  the  walls  of  the  ascocarp  peculiar  arms 
extend,  and  in  the  lilac  mildew  and  some  other  kinds  these 
have  strikingly  branched  tips,  which  sometimes  serve  as  one 
means  of  distinguishing  the  species. 


FIG.  186.  The  spore-sac  case  of  lilac 
mildew  (Microsphcera  alni) 

The  central,  heavy-walled  body  (ascocarp) 
contains  the  sacs  (asci)  in  which  spores  are 
formed.  Upon  the  wall  of  the  ascocarp  are 
stalks,  sometimes  called  arms,  which  have 
peculiar  branches  at  their  tips.  About  60 
times  natural  size 


THE  SAC  FUNGI  (ASCOMYCETES) 


231 


O, 


The  heavy-walled  ascocarp  is  resistant  to  unfavorable  cli- 
matic conditions,  and  may  pass  through  the  winter  and  in  the 
following  spring  break  open,  thus  freeing  the  thin-walled  asci. 
Upon  escaping,  the  spores  may  be  blown  or  carried  about  and 
germinate  upon  new  host  leaves. 

224.  Blue  mold  or  green  mold  (Penicillium).  This  mold  fre- 
quently appears  upon  discarded  leather,  upon  shoes  or  gloves 
which  when  damp  have  been  left  in  a 
dark  warm  place,  upon  old  lemons,  and 
upon  cheese  and  other  dairy  products. 
Various  species  have  distinct  shades 
of  color,  so  that  the  common  names  of 
blue  or  green  mold  can  be  taken  only 
as  applying  in  a  general  way.  Certain 
species  of  Penicillium  are  supposed  to 
give  characteristic  flavors  to  cheese 
in  which  they  grow,  as  Penicillium 
Roqueforti  of  Roquefort  cheese  and 
Penicillium  Camemberti  of  Camembert 
cheese.  These  species  are  widely  dis- 
tributed, however,  and  are  found 
growing  upon  many  substances  other 
than  cheese.  It  has  been  suggested 
that  these  are  not  different  species, 
but  that  they  merely  show  different 
features,  dependent  upon  the  kind 
of  material  upon  which  they  grow. 
While  it  is  true  that  these  as  well  as  species  of  other  molds  do 
show  different  characteristics  when  grown  in  different  ways, 
recent  investigations  indicate  that  the  species  are  distinct.1 

Penicillium  is  an  ascomycete  which  has  almost  lost  the 
habit  of  reproduction  by  means  of  ascospores,  the  ascus  being 

1  An  interesting  discussion  of  various  species  and  their  cultural  reac- 
tions is  "  Cultural  Studies  of  Species  of  Penicillium,"  by  Charles  Thorn, 
Ph.D.,  Mycologist  in  Cheese  Investigations,  Bulletin  148,  Bureau  of  Animal 
Industry,  U.  S.  Dept.  Agr.,  1910. 


FIG.  187.  The  blue  mold 
(Penicillium) 

At  the  left  is  the  tip  of  a  hy- 
pha,  with  the  characteristic 
branches,  on  the  ends  of  which 
are  the  spores;  at  the  right 
are  germinating  spores.  After 
Thorn.  Much  magnified 


232  PRACTICAL  BOTANY 

rarely  formed.  It  reproduces  itself  very  .abundantly  by  means 
of  conidia.  Plants  branch  profusely  at  their  ends,  and  from 
the  tips  of  these  branches  conidia  are  formed  (Fig.  187).  The 
number  of  these  conidia  is  often  so  large  that  when  the  sub- 
stance supporting  the  plants  is  slightly  shaken  a  small  cloud 
of  spores  arises. 

225.  Yeasts.  The  yeasts  (Saccharomycetes)  constitute  a  group 
of  plants  of  somewhat  doubtful  classification.  Since  occasion- 
ally they  form  an  ascus-like  sac  in  which  spores  are  formed, 

they  are  often  classed  with 
the  ascomycetes.  They  are 
extremely  simple,  and  are 
more  interesting  because  of 
their  manner  of  life  than 
because  of  their  structure. 

A  yeast  plant  is  a  single  cell 
FIG.  188.  Yeast  plants  (Saccharomycetes)         _» 

(Fig.  188).  It  usually  repro- 

a,  a  plant  from  which  a  bud  has  begun        2  .    '  ,„    ,  ,11 

to  grow;  b  and  c,  plants  with  two  buds,     duces    itself   by  a  method 

Note  the  vacuoles  in  the  plants.   Greatly       of    vegetative    reproduction 

known    as    budding.     The 

buds,  before  becoming  separated  from  the  parent  cells,  may 
bud  again-  and  again  until  a  chain  of  plants  is  formed.  If  a 
cake  of  commercial  yeast  is  examined,  it  is  found,  in  addition  to 
the  large  starch  grains  nearly  always  occurring  in  yeast  cakes, 
to  consist  of  thousands  of  yeast  cells,  some  single  and  some  in 
process  of  budding.  If  a  cake  of  yeast  is  kept  at  room  tempera- 
ture, the  plants  soon  continue  their  growth,  and  other  organisms 
(bacteria  and  molds)  also  grow,  so  that  the  yeast  "  spoils." 

When  yeast  plants  are  placed  in  dough  they  grow  with 
great  rapidity.  They  live  upon  the  solutions  in  the  dough, 
and  in  so  doing  break  down  the  sugar,  thus  forming  from  it 
small  quantities  of  alcohol  and  carbon  dioxide.  The  carbon- 
dioxide  gas  forms  the  "air  spaces"  in  the  dough,  which  cause 
the  phenomena  known  as  "  rising."  1  In  cooking  the  dough 

1  Salt-rising  bread  owes  its  peculiar  quality  to  the  fact  that  instead  of 
yeasts  certain  bacteria  produce  a  putrefactive  fermentation  within  the  dough. 


THE  SAC  FUNGI  (ASCOMYCETES)  233 

the  air  spaces  are  enlarged  and  at  the  same  time  the  alcohol 
is  evaporated.  In  former  methods  of  bread  baking  pure  cul- 
tures of  yeast  were  less  likely  to  be  secured, — "  wild  "  yeasts 
very  frequently  appearing.  With  modern  methods,  quite  sim- 
ilar to  those  used  in  bacteriology,  pure  cultures  may  be  ob- 
tained, and  it  is  therefore  possible  to  secure  the  exact  kind  of 
fermentation  of  the  dough  that  is  desired.1 

The  processes  of  fermentation  by  yeasts  are  used  in  the 
manufacture  of  alcohol,  wine,  beer,  and  other  liquors  which 
contain  alcohol.  Certain  definite  kinds  of  yeasts  produce  cer- 
tain kinds  of  alcoholic  fermentation,  and  it  is  necessary  for 
the  brewer  to  keep  pure  cultures  of  the  desired  yeasts  in  order 
to  insure  the  particular  quality  of  his  product.  It  is  worthy 
of  note  that  the  difficulties  which  brewers  formerly  had  from 
impure  yeasts  furnished  the  occasion  for  the  development  of 
the  basis  of  modern  bacteriology.  The  brewers  of  Germany 
appealed  to  the  great  scientist,  Louis  Pasteur,  to  assist'  them 
in  this  difficulty.  He  succeeded,  in  1856,  in  devising  methods 
of  pure  culture  by  isolating  single  yeast  plants  and  growing 
a  colony  from  each.  Thus  the  particular  result  to  be  secured 
could  be  determined  by  the  kind  of  yeast  selected  for  use 
in  fermentation.  It  was  this  method  of  pure  culture  which 
opened  the  way  for  bacteriological  investigations. 

226.  Other  ascomycetes.  The  number  of  destructive  asco- 
mycetes  is  too  large  even  to  be  enumerated  in  this  elemen- 
tary treatise.  Some  of  the  more  important  ones  besides  those 
discussed  above  are  here  given.  Upon  heads  of  rye  the  dis- 
ease known  as  ergot  (Claviceps purpurea)  sometimes  develops. 
Its  mycelium  infests  the  whole  plant.  Within  and  about  the 
developing  grains  masses  of  summer  spores  are  formed.  Later 
the  same  mycelium  produces  dark  compact  masses  (Fig.  189), 
which  completely  replace  some  of  the  grains.  These  fall  to  the 
ground  and  lie  dormant  through  the  winter,  and  from  them  in 
the  spring  the  ascospores  for  new  growth  develop.  The  spore 

1  An  especially  interesting  paper  is  "Bread  and  the  Principles  of  Bread 
Making,"  by  Helen  W.  Atwater,  Farmers'  Bulletin  11%,  U.  S.  Dept.  Agr.,  1900. 


234 


PRACTICAL  BOTANY 


masses  are  poisonous,  and,  as  ergotine,  are  sometimes  used  for 

medicinal  purposes.  A  parasite  known  as  root  rot  (  Thielavia  la- 
sicola)  attacks  the  roots  of  tobacco,  horse- 
radish, and  violets,  and  of  peas  and  other 
leguminous  plants.1  The  rose  and  peach 
mildew  (Sphoerotheca  pannosa)?  which  oc- 
casionally appears  as  light-colored  downy 
patches  upon  the  fruit  of  the  peach,  attacks 
the  leaves  of  roses  and  is  very  destructive. 
The  wilt  disease  of  cotton,  cowpea,  and 
watermelon  (Neocosmospora  vasinfecta)  3  is 
widely  distributed  over  the  Southern  states 
and  attacks  the  vascular  bundles  in  such  a 
way  as  to  cut  off  the  plant's  water  supply. 
A  common  disease  of  plum  and  cherry 
trees  is  black  knot  (Plowrightia  morbosa).4 
The  familiar  and  very  destructive  dark 
and  shrunken  patches  on  the  fruit  of  the 
apple  are  due  to  bitter  rot  {Grlomerella 
rufomaculans)?  The  value  of  fruit  des- 
troyed by  it  sometimes  amounts  to  millions 
of  dollars  in  a  single  year. 

In  addition  to  the  conidial  forms  already 
considered  in  connection  with  their  asco- 
sporic  forms  and  used  as  types  of  their  re- 
spective groups,  there  remain  thousands  of 
species  whose  life  histories  are  not  known. 

Many  are  saprophytes  and  many,  are  parasites,  some  of  which 

are  very  destructive  to  crops. 

1  Clinton,  G.  P.,  "Root  Rot  of  Tobacco,"  Conn.  Agr.  Exp.  Sta.,  1906. 

2  "Peach  Mildew,"  Bulletin  107,  Colo.  Agr.  Exp.  Sta.,  1906. 

8  "Wilt  Disease  of  Cotton,  Watermelon,  and  Cowpea,"  Bulletin  17,  Divi- 
sion of  Vegetable  Pathology,  U.  S.  Dept.  Agr.,  1899. 

*Lodeman,  E.  G.,  "Black  Knot,"  Bulletin  81,  Cornell  University  Agr. 
Exp.  Sta.,  1894. 

6  "The  Bitter  Rot  of  Apples,"  Bulletin  44,  Bureau  of  Plant  Industry, 
U.  S.  Dept.  Agr.,  1903. 


FIG.  189.  Ergot  which 
has  grown  on  a  head 

of  rye 
After  Duggar 


THE  LICHENS  235 

LICHENS 

227.  General  characteristics.  The  lichens  are  not  simply 
fungi.  A  lichen  is  not  even  a  single  plant,  but  is  a  com- 
bination of  fungi  and  algae  living  together  in  such  a  close 
relationship  that  it  looks  like  a  single  plant.  There  may  be 
many  individual  fungi  and  many  individual  algae  in  this  rela- 
tion, but  the  combination  is  spoken  of  as  the  lichen  plant. 
The  fungal  part  of  the  lichen  is  usually,  though  not  always,  a 
member  of  the  ascus-bearing  class  of  fungi,  and  consequently 
lichens  are  often  classified  with  ascomycetes.  This  is  obvi- 
ously a  somewhat  questionable  classification,  but  for  lack  of 
a  better  one  we  shall  dis- 
cuss the  class  in  this  con- 
nection. The  algae  that 
enter  into  the  formation 
of  lichens  are  usually  uni- 
cellular forms  resembling 
Pleurococcus,  but  may  be 
filamentous  green  algae  or 
even  some  of  the  blue- 
o-TAon  alrr»  FlG- 19°-  A  foliaceous  lichen  (Parmelia) 

LiJ.v?"ll    CtJ.fi  ct%  ,  _  _         , 

3   T  .  ,          , .  ,      ,  upon  a  piece  of  bark 

Lichens  live  upon  bark  ^  ,     ,  . 

*  .Natural  size 

of  trees,  stones,  and  upon 

soil  (Fig.  190).  They  thrive  under  conditions  of  exposure  and 
in  moisture  and  temperature  variations  which  do  not  permit 
most  plants  to  grow.  They  are  found  at  as  great  altitudes 
and  with  as  great  range  north  and  south  as  any  plants. 

In  "stony  places  lichens  often  form  heavy  mats  made  up 
of  lichen  bodies,  mosses,  and  decomposed  rock.  These  masses 
when  upon  upright  faces  of  rock  may  by  their  own  weight 
fall  and  become  the  soil  for  growth  of  other  plants.  New 
growths  soon  start  where  the  old  ones  were,  and  by  a  con- 
tinuation of  this  process  these  plants  may  slowly  wear 
away  large  masses  of  stone.  It  is  probable  that  consider- 
able chemical  action  is  exerted  upon  the  rock  by  the  hyphae, 


236 


PEAGTICAL  BOTANY 


resulting  in  decomposition  of  the  substratum.  Examination 
of  almost  any  stone  pile  that  is  but  a  few  years  old  will 
show  the  presence  of  these  forerunners  of  other  plant  life. 
x  ^  We  have,  therefore,  a  combination 

of  alga  and  fungus,  neither  of 
which  alone  could  keep  alive 
in  places  of  such  great  ex- 
posure, living  together 
and  instrumental  in 
building  up  soil 
where  at  first 
no  other 
plants 
could 
live. 


FIG.  191.  A  hanging  lichen  (Usnea)  which  is 
often  called  the  "bearded  moss."  Also  upon 
the  dead  spruce  twig  which  supports  this  lichen 
there  is  another  foliose  lichen  (Parmelia).  Upon 
the  Usnea  plant  there  are  shown  several  of  the 
disk-like  cups  in  which  ascospores  are  formed 


228.  Form,  structure,  and  reproduc- 
tion. Those  lichens  which  adhere  like 
leaves  to  the  material  upon  which  they 
grow  are  called  foliose  (Fig.  190) ;  those 
that  form  closely  adhering,  scale-like 
growths  are  crustaceous  forms;  "those 
that  branch  and  are  partially  free  from 
the  substratum  swefruticose  (Fig.  191); 
while  a  few  are  mucilaginous  or  ge- 
latinous forms.  Foliose  forms  are  com- 
mon upon  the  rougher-barked  trees, 
fences,  etc. ;  crustaceous  forms  grow 
upon  smooth-barked  trees  and  upon 


THE  LICHEFS 


237 


stones ;  while  fruticose  forms  grow  upon  the  ground  or  hang 
from  branches  of  trees.  Illustrations  of  the  latter  group  are 
the  reindeer  moss  (Gladonia  rangiferina)  and  other  cladonias 
(Fig.  193),  and  the  bearded 
moss  (Usnea  barbata). 

In  sections  or  carefully 
made  dissections  of  a  lichen 
body  usually  the  fungus  is 
seen  to  compose  the  outer 
covering  for  the  whole  body. 
The  algae  are  within,  and 
often  closely  wound  about 
by  the  hyphae  of  the  fungi 
(Fig.  194),  which  absorb 
food  from  the  cells  of  the 
algae. 

The  fruiting  cups  usu- 
ally resemble  some  of  those 
of  the  ascomycetes.  Within 
the  base  of  the  cup  in  most 
lichens  the  fungal  hyphse 
form  asci  and  ascospores,  as 
do  many  ascomycetes.  These 
spores  belong  to  the  fungus. 
The  algal  part  of  the  lichen 
when  it  is  a  one-celled  alga 
like  Pleurococcus  reproduces 
by  division,  as  we  have  al- 
ready found  that  it  does  in 
the  green  algae.  This  repro- 

.  c  The  branches  hear  the  fruiting  cups,  and 

auction    01    the    alga   OCCUrs  branches  may  also  grow  from  the  cups, 

quite    independently   of  the  The  open  sides  of  the  cups  are  shown  in  6, 

J  and  the  reverse  surfaces  m  c 

reproduction  of  the  fungus. 

229.  Economic  importance  of  lichens.  Probably  the  greatest 
economic  importance  of  lichens  is  found  in  their  relation  to 
formation  of  soils.  Any  freshly  bared  rock  soon  becomes  the 


FIG.  192.  A  detail  of  a  small  piece  of 
Usnea  barbata 


238 


PRACTICAL  BOTANY 


home  of  small  crustaceous  lichens.  As  these  grow,  die,  and 
decay,  and  are  replaced  by  others  of  their  kind,  the  living  and 
decaying  bodies  tend  to  disorganize  the  rock.  Weathering 
processes  also  assist  in  crumbling  the  rock,  and  after  a  time 
there  is  soil  enough  to  permit  the  growth  of  other  lichens  and 
mosses  and  finally  of  larger  plants.  These  pioneer  plants  are 

eventually  driven 
from  the  rock  by 
others  that  can 
live  in  the  meager 
soil  that  is  pro- 
duced by  the  li- 
chens and  mosses. 
Certain  kinds  of 
crustaceous  lichens 
are  looked  upon 
as  the  forerunners 
of  higher  vegeta- 
tion in  rocky  re- 
gions which  are 
too  bare  to  per- 
mit other  forms 
of  vegetation  to 
live.  They  are 
almost  universally 
distributed  over 
the  earth.  The 

time  required  for  the  production  of  soil  sufficient  for  the  growth 
of  other  plants  depends  largely  upon  the  nature  of  the  rock 
and  upon  the  climate.    Upon  some  lava  beds  it  is  said l  that 
after  almost  two  hundred  years  from  their  formation  crusta- 
ceous lichens  in  places  are  still  the  only  plants  to  be  found. 
Lichens  as  food  for  herbivorous  animals  are  of  considerable 
importance  in  regions  where  other  foods  are  scanty  or  where 
for  parts  of  the  year  cold  and  snow  render  other  vegetation 
1  Warming,  CEcology  of  Plants,  chap.  xvii. 


FIG.  193.  A  cup  lichen  (Cladonia) 

This  lichen  often  appears  on  moist  ground,  and  at  times 

forms  the  cup-like  reproductive  bodies,  even  sometimes 

having  some  of  these  form  upon  other  cups.  Two  and 

one-half  times  natural  size 


THE  LICHENS  239 

unavailable.  Reindeer  moss  (Cladonia  rangiferina)  grows  upon 
earth  and  rocks  in  great  abundance  throughout  the  north  tem- 
perate and  frigid  zones,  and  at  high  altitudes  in  most  mountain 
ranges.  In  winter  it  is  eaten  by  animals,  which  find  it  green  and 
nutritious  when  they  remove  the  snow  from  above  it. 

A  few  lichens  are  sometimes  used  as  food  for  men,  though 
they  are  not  especially  nutritious.  A  mucilaginous  and  starchy 
food  is  prepared  from  Cetraria  islandica,  a  lichen  which  is 
known  as  Iceland  moss.  This  and  other  food  lichens  are  more 
or  less  bitter,  and  when  used  regularly  in  large  quantities  are 


FIG.  194.  A  small  piece  of  a  lichen,  showing  in  detail  the  relation  that  exists 
between  the  mycelium  of  the  fungus  (/)  and  the  algal  cells  (a)   . 

Magnified  500  diameters.  After  Bonnier 

said  to  have  caused  disagreeable  intestinal  disturbances.  Other 
lichens  have  been  ground  with  wheat  in  making  wheat  flour, 
as  in  parts  of  northern  Africa.  The  lichens,  while  adding  some 
nutrient  matter,  also  add  considerable  non-nutritious  calcare- 
ous material,  so  that  altogether  the  bulk  of  the  flour  is  in- 
creased at  the  expense  of  the  quality.  In  Sweden  one  very 
bitter  lichen  (Sticta  pulmonacea)  is  sometimes  used  as  a  sub- 
stitute for  hops  in  processes  of  brewing. 

Various  dyes  are  prepared  from  lichens.  These  were  once 
more  commonly  used  than  they  are  to-day,  and  are  known  in 
the  markets  under  the  names  of  orchil  and  cudbear.  Litmus, 
used  in  preparing  litmus  or  blue  test  paper,  a  common  and 
fairly  delicate  test  for  the  presence  of  acids,  is  prepared  from 
lichens. 


240 


PRACTICAL  BOTANY 


BASIDIOMYCETES 

230.  Different  groups  of  basidiomycetes.  The  prominent 
groups  of  basidiomycetes  are :  the  smuts,  which  frequently  ap- 
pear in  the  heads  of  oats,  wheat,  and  barley,  and  upon  the  ears 
and  stalks  of  corn;  rusts,  which  are  universally  distributed 
wherever  wheat  is  grown,  and  which  also  grow  upon  many 

other  hosts ;  the  toadstools, 
mushrooms,  and  puffballs. 
Next  to  the  ascomycetes, 
this  is  the  largest  class  of 
fungi,  and  is  one  of  great 
economic  importance. 


FIG.  195.  Sprays  of  oat  plants  (Avena  sativa) 

The  grass-like  leaf  character  I  is  well  known  in  this  plant ;  the  plant  at  the  left 

has  developed  normally,  while  in  that  at  the  right  the  grains  have  been  destroyed 

and  replaced  by  oat  smut  and  the  growth  of  the  entire  plant  is  checked.  Both  one 

third  natural  size 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      241 

231.  The  smuts.  All  the  smuts  are  parasitic.  They  are  par- 
ticularly destructive  to  the  grains  and  are  widely  distributed. 
In  the  United  States  it  is  estimated  that  the  injury  caused  by 
smuts  to  wheat,  oats,  and  barley  exceeds  $25,000,000  annually. 
The  oat  smut  (TJstilago  Avence)  is  present  in  almost  every 
field  of  oats.  It  is  generally  recognized  by  means  of  the  black 
sticky  masses  of  spores  that  form  in  the 
positions  previously  occupied  by  the  devel- 
oping grains  (Fig.  195).  The  spore  mass, 
however,  is  the  external  indication  that  the 
smut  mycelium  has  previously  permeated 
the  host.  The  smut  usually  matures  at 
about  the  time  the  oat  heads  are  in  full 
flower,  and  prevents  the  normal  develop- 
ment to  such  an  extent  that  the  annual 
damage  in  this  country  is  estimated  to 
reach  $6,500,000.  Upon  germination  of 
these  heavy-walled  spores  a  short  hypha 
is  produced.  This  soon  produces  four 
thin-walled  spores  (Fig.  196).  Since  these 
thin-walled  spores  appear  at  about  the 
same  time  that  oat  seedlings  are  growing, 
they  produce  hyphae  which  penetrate  the 
host  plant.  Under  favorable  growing  con- 
ditions the  smut  mycelium,  which  contin- 
ues its  growth  throughout  the  host,  does 
not  markedly  retard  the  growth  of  the  infected  oat  plants. 

The  spores  that  are  formed  in  the  heads  have  heavy  resistant 
walls.  They  may  adhere  to  the  grains,  lie  in  the  granaries,  or 
lie  upon  the  ground  in  the  fields  until  favorable  conditions  for 
growth  occur.  Probably  the  grain  used  for  seed  is  itself  one  of 
the  chief  means  of  spore  distribution.  It  has  been  found  that  by 
treating  seed  oats  with  hot  water  (132°  to  133°F.),  or  with  water 
containing  four  tenths  per  cent  formalin,  the  smut  may  be  killed.1 

1  "  The  Grain  Smuts,"  Farmers'  Bulletin  75,  U.  S.  Dept.  Agr.,  1898;  "The 
Smuts  of  Grain  Plants,"  Bulletin  122,  Minn.  Agr.  Exp.  Sta.,  1911. 


FIG.  196.  A  stage  In 

the  loose  smut  of  oats 

(Ustilago  Avence) 

The  small  hypha  that 
is  produced  by  the  ger- 
minating spore  soon 
produces  bud-like  co- 
nidia.  Greatly  magni- 
fied. After  Duggar 


242 


PEACTICAL  BOTANY 


sm 


Corn  smut  ( Ustilago  Zece)  infests  many  of  the  corn  plants 
in  an  ordinary  field,  and  when  abrasions  of  the  plants  occur 
the  unattractive  smut  masses  frequently  appear.  They  most 

often  appear  in  the 
tassel  or  ear,  and 
may  completely  or 
partially  destroy 
both  (Fig.  197).1 

232.  The  rusts. 
The  intricate  struc- 
tures and  habits  of 
living  of  the  rusts 
are  objects  of  great 
interest  to  bota- 
nists. Their  effect 
upon  useful  and 
decorative  plants 
that  serve  as  their 
hosts  gives  them 
great  economic  im- 
portance. A  given 
species  of  rust  may 
live  for  a  time  upon 
one  kind  of  plant 

„  and  later  upon  host 

FIG.  197.  An  ear  of  corn  within  and  upon  which 

corn  smut  (Ustilago  Zece)  has  grown 


The  bracts  which  inclose  the  ear  (E)  have  peculiar 

leaf-like  extensions  of  their  tips.  Masses  of  the  spores 

of  the  smut  (sm)  have  grown  and  extruded  at  the  tip 

of  the  ear 


plants  that  belong 
to     other    groups. 
In    each   of    these 
stages  the  parasite 
has  distinctly  dif- 
ferent structures  and  produces  quite  different  effects  upon 
its  host.    So  unlike  are  these  stages  that  formerly  they  were 
named  as  distinctly  different  plants,  and  it  is  only  recently 
that  enough  has  been  learned  about  them  to  enable  us  to 
know  some  of  the  different  appearances  they  may  assume. 
1  "  Corn  Smut,"  Ind.  Agr.  Exp.  Sta.,  1900. 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      243 


233.  Black  rust  of  grain  (Puccinia  graminis).  Wherever  wheat 
and  oats  are  grown,  black  rust,  sometimes  called  red  rust,  is  a 
dreaded  pest.  It  also  grows  upon  many  other  grasses,  includ- 
ing barley  and  other  cereals.  The  damage  done  to  the  world's 
crops  by  this  fungus  is  very  large  indeed,  and 
in  the  United  States  it  has  been  estimated  to 
exceed  $15,000,000  in  a  single  year.  Much 
money  has  been  expended  in  making  stud- 
ies of  the  life  habits  of  this  parasite,  with 
the  hope  that  means  of  preventing  its  ravages 
may  be  discovered. 

The  first  conspicuous  appearance  of  rust 
in  the  late  spring  or  early  summer  is  in  the 
form  of  reddish-brown  patches  upon  stalks 
and  leaves  of  wheat  and  oats  (Fig.  198).  The 
patches  are  composed  of  large  numbers  of 
"summer  spores"  (uredospores').  A  section  cut 
through  the  host  leaf  (Fig.  199,  A~)  enables 
one  to  see  that  the  uredospores  are  formed 
upon  the  ends  of  hyphae.  The  spore-bearing 
ends  of  hyphaB  are  continuations  of  hypha3 
which  have  pushed  their  way  among  the  leaf 
cells  from  which  they  have  absorbed  their 
nourishment.  At  the  time  uredospores  are 
formed  the  host  plant  is  usually  thoroughly 
infested  with  the  mycelium.  The  uredospores 
are  readily  carried  about  by  currents  of  air 
or  contact  with  animals.  If  placed  upon  wheat 
or  oat  plants,  these  spores  germinate,  and  the 
young  hyphse  penetrate  the  host  and  produce 
new  mycelium. 

Later  in  the  summer  the  same  mycelium 
which  produced  uredospores  may  produce  a 
heavy-walled  two-celled  spore  (Fig.  199,  (?) 
known  as  the  "  winter  spore  "  (teleutospore). 
When  formed  in  large  quantities  these  spores 


FIG.  198.  Apiece 
of  a  stalk  of  wheat 
upon  which  spots 
of  the  rust  para- 
site have  formed 


FIG.  199.  Black  rust  (Puccinia  graminis) 

A,  A  small  section  of  a  wheat  leaf  upon  which  the  parasitic  rust  is  growing: 
ra,  mycelial  hyphae  of  the  rust;  y.  tt,  young  summer  spore,  or  uredospore;  u,  fully 
formed  uredospore ;  st,  upright  hypha  upon  which  uredospore  is  formed.  B,  ger- 
mination of  uredospore:  st,  old  hypha;  u,  old  uredospore  wall ;  m,  new  mycelial 
hyphae.  C,  winter  spore,  or  teleutospore :  st,  hypha;  t,  two-celled  spore.  D,  ger- 
mination of  teleutospore:  st,  old  hypha;  p,  new  hypha,  or  the  promycelium ; 
s,  spores  or  sporidia.  E,  section  of  the  barberry  leaf  showing  secidiospore  stage 
of  rust:  ej  upper  epidermis,  and  e2  lower  epidermis;  p,  wall  of  cup  or  aecidium; 
s,  aecidiospores.  Rearranged  from  Duggar's  "Fungous  Diseases  of  Plants."  All 

much  enlarged 
244 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      245 

appear  as  blistery  patches,  much  like  those  made  by  the  red- 
dish spores  except  for  the  difference  in  color.  The  teleuto- 
spores  are  scattered  over  the  ground  and  upon  wheat  and 
oat  straw.  After  a  period  of  dormancy,  usually  lasting 
through  the  winter,  these  spores  germinate.  From  each  cell 
of  the  teleutospore  in  the  spring  there  grows  a  small  hypha 
(Fig.  199,  Z>),  quite  resembling  the  one  which  grows  from 
the  smut  spore  (Fig.  196).  Similarly,  each  cell  of  this  hypha 
may  form  one  of  the  thin-walled  spores  (sporidia). 

Puccinia  graminis  sometimes  has  another  stage  in  its  life 
cycle.  In  regions  —  as  in  the  New  England  States  —  where 
a  shrub  known  as  barberry  is  common,  the  sporidia  when 
alighting  upon  leaves  of  the  barberry  may  grow  and  produce 
within  the  leaf  an  extensive  growth  of  mycelium.  When 
this  mycelium  produces  spores,  they  appear  in  a  peculiar  cup 
on  the  underside  of  the  barberry  leaf  (Fig.  199,  E).  These 
spores,  being  different  from  any  of  the  three  described  and 
being  formed  in  a  cup,  are  called  cecidiospores,  or  cup  spores. 
jEcidiospores  may  reproduce  the  rust  plant  upon  wheat 
and  oats.  When  the  life  cycle  of  black  rust  was  discovered, 
it  was  thought  that  all  four  stages  are  essential  to  it.  It  is 
now  known,  however,  that  the  barberry  stage  may  sometimes 
be  omitted.  The  native  barberry,  not  the  Japanese  variety, 
is  the  one  on  which  this  rust  grows,  and  efforts  are  being 
made  to  destroy  this  plant  with  the  hope  of  reducing  the 
rust  disease  on  wheat  and  oats.  Uredospores  persist  through 
the  winter  in  sufficient  quantity  to  reproduce  the  rust  upon 
oats  and  wheat  in  the  following  spring.  No  satisfactory  pre- 
ventive for  this  fungus  has  been  discovered.  Some  progress 
has  been  made  by  learning  which  varieties  of  wheat  and  oats 
are  most  resistant  to  attacks  by  the  parasite.1 

234.  Other  rusts.   Upon  the  leaves  and  stems  of  carnations 

an  injurious  rust  (  Uromyces  caryophyllinus)  sometimes  appears. 

Asparagus  rust  {Puccinia  Asparagi),  probably  introduced  into 

this  country  from  Europe  but  a  few  years- ago,  is  now  generally 

1  "Rusts  of  Cereals,"  Bulletin  109,  S.  Dak.  Agr.  Exp.  Sta.,  1908 


246 


PEACTICAL  BOTANY 


distributed  over  asparagus  beds.1  The  hollyhock  and  many 
other  members  of  the  mallow  family  (Ma&vacecey,  to  which  the 
hollyhock  belongs,  are  often  all  but  destroyed  by  the  holly- 
hock rust  (Pucdnia  Malvacearum).  ^Ecidial  stages  of  other 
rusts  appear  upon  many  common  plants,  as  the  May  apple, 
jack-in-the-pulpit,  burdock,  sunflower,  and  blackberry. 

Apple  rust  and 
"  cedar  apples," 
produced  by  the 
rust  Grymnospo- 
rangium  macro- 
pus,  offer  a  strik- 
ing life  cycle. 
Upon  red  cedar 
trees  in  the  late 
autumn,  winter, 
and  early  spring 
branches  may  be 
found  with  hard 
brownish  knots 
upon  them  (Fig. 
200).  The  knots 
are  outgrowths 
produced  by  the 
internal  myceli- 
um of  the  rust. 
Near  or  before  the  period  in  the  spring  when  apple  trees  are  in 
flower  or  setting  young  fruit,  the  brownish  knots  or  "  cedar 
apples"  become  gelatinous,  and  from  them  yellow  projec- 
tions protrude  (Fig.  201).  These  projections  are  made  up 
of  hyphse  bearing  teleutospores.  The  teleutospores  germinate 
at  once,  producing  from  one  to  three  hyphse  from  each  cell. 
Sporidia  are  formed,  and  since  these  are  blown  about  in  great 
profusion,  some  of  them  alight  upon  young  leaves,  flowers,  or 

1  "The  Asparagus  Rust:  its  Treatment  and  Natural  Enemies,"  Bulletin 
129,  N.  J.  Agr.  Exp.  Sta.,  1898. 


FIG.  200.  A  " cedar-apple"  parasite  (Gymnosporan- 

gium)  as  it  appears  in  winter  condition  upon  its  host, 

the  red  cedar  (Juniperus  Virginiana) 

Natural  size 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      247 

fruit  of  the  apple  tree,  or  other  members  of  the  apple  family. 
The  apple  tree  is  thus  infected,  and  during  the  summer  the 
cups  bearing  secidiospores  are  formed.  Some  of  the  secidio- 
spores  may  fall  upon  the  cedar  and  reinfect  that  host.  In 
late  summer  and  autumn  "cedar  apples"  are  again  produced.1 

235.  Toadstools  and  mush- 
rooms. These  fungi  are  char- 
acterized in  general  by  the  fact 
that  the  mycelium  lives  entirely 
within  the  material  which  fur- 
nishes its  nourishment,  and  oc- 
casionally sends  up  into  the  air 
the  spore-bearing  structure  that 
is  called  the  toadstool  or  mush- 
room. Scientifically  there  is  no 
accepted  distinction  between 
toadstools  and  mushrooms. 

Those  forms  that  are  known 
to  be  good  to  eat  are  popularly 
spoken  of  as  mushrooms,  while 
those  that  are  not  edible,  or 
that  are  poisonous,  are  called 
toadstools.  Even  this  distinc- 
tion, which  is  wholly  popular 
and  was  made  solely  upon  the 
basis  of  real  or  supposed  edibil- 
ity, is  not  easily  applied,  since  little  is  known  regarding  the 
edibility  of  many  species.  Furthermore,  in  a  given  genus  some 
species  may  be  excellent  for  food,  and  others  poisonous.  Cer- 
tain edible  species  are  easily  learned  and  are  not  readily  con- 
fused with  those  which  are  poisonous.2  There  are  over  one 
thousand  edible  fungi  which  grow  in  the  United  States. 

1  "The  Cedar-Apple  Fungi  and  Apple  Rust  in  Iowa,"  Bulletin  84,  Iowa 
Agr.  Exp.  Sta.,  1905. 

2  The  United  States  Department  of  Agriculture  publishes  several  bulle- 
tins upon  poisonous  and  edible  fungi. 


FIG. 201.  A  "cedar  apple "(Gymno- 
sporangium)  in  its  spring  condition 

The  extrusions  are  made  up  of  hyphae 
and  teleutospores.  Three  eighths  nat- 
ural size 


248 


PRACTICAL  BOTANY 


236.  Toadstools  and  mushrooms  :  structure  and  reproduction. 
The  mycelium  often  becomes  very  extensive,  and  may  form 
moldy  or  cobweb-like  threads  within  the  rich  earth,  decaying 
wood,  or  other  nourishing  substratum.  When  it  grows,  the 
mycelium  helps  to  bring  about  the  decay  of  the  material  which 
nourishes  it,  and  therefore  may  be  very  destructive.  The 


FIG.  202.  A  large  toadstool 
Note  the  stalk,  the  ring,  the  crown,  and  the  gills.   One  third  natural  size 

mushroom  spawn,  which  is  sometimes  especially  prepared  and 
sold  in  bricks  to  those  who  wish  to  grow  mushrooms,  is  sim- 
ply a  mass  of  mycelium.  At  times  there  form  aggregations 
of  the  mycelium,  which  are  whitish,  bud-like  growths  called 
"  buttons,"  and  which  are  the  beginnings  of  the  structures 
known  as  toadstools  or  mushrooms.  They  grow  and  push  their 
way  to  the  surface.  As  the  "button"  elongates,  its  top  begins 
to  expand  into  the  umbrella-like  form,  and  finally  opens  out 
as  the  crown  or  pileus,  with  its  center  attached  to  the  upper 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      249 


FIG.  203.  Gills  of  a 
toadstool 

On  the  faces  of  the  gills 
the  spores  are  formed. 
Seven  and  one-half  times 
natural  size.  After  Buller 


end  of  the  stalk  (stipe)  (Fig.  202).    As  the  pileus  opens,  it  is 

joined  to  the  stalk  beneath  by  means  of  a  layer  of  hyphse  (the 
veil).  This  in  some  species,  in  breaking 
away  from  the  pileus,  forms  a  ring  or 
annulus  about  the  stalk. 

The  underside  of  the  pileus  is  made 
up  of  plate-like  growths  (jjills),  which 
radiate  from  the  point  of  attachment  to 
the  stalk.  The  flat  surfaces  of  the  adja- 
cent plates  face  one  another  (Fig.  203). 
Some  of  the  hyphse  which  compose  the 
gills  grow  in  such  a  way  that  their  tips 
extend  a  little  way  from  the  surface  of 
the  gill.  Upon  this  extended  tip  (ba- 
sidium)  four  (rarely  two)  branches  are 
formed,  and  upon  the  tip  of  each  branch 
a  spore  (basidiospore)  is  formed  (Fig. 
204).  When  the  spores  fall  upon  moist, 

warm,  nutrient  material,  they  produce  a  new  mycelium.    By 

cutting  the  pileus  of  a  ripe  toadstool  from  the  stalk  and  placing 

it  with  the  gills  downward  upon 

a  piece  of  ordinary  white  or  black 

paper,  after  a  few  hours  there  will 

be  made  a  "spore  print"  composed 

of  thousands  of  spores. 

237.  Toadstools  and  mushrooms: 

different  forms  and  habits.  The  type 

form  just  described  is  representa- 
tive of  the  most  common  toadstools 

&iid  mushrooms.    The  commonest 

Cultivated  mushroom  (Agaricus  cam- 

pestris)  has  long  been  a  well-known 

article  of  food.    Some  of  the  same 

type  of  toadstools  form  "  fairy  rings "  (Figs.  205  and  206), 

which  in  constantly  widening  circles  may  appear  in  the  same 

locality"  year  after  year.    The  phenomenon  is  doubtless  due 


FIG.  204.  Basidia  arid  spores 
of  a  toadstool 

Three  hundred  seventy  times 
natural  size.   After  Buller 


FIG.  205.  A  group  of  toadstools 
Note  the  stalk,  crown,  ring  about  the  stalk,  and  the  gills 


FIG.  206.  A  "fairy  ring"  formed  by  toadstools 

This  ring  appeared  with  successively  widening  circles  for  at  least  six  years.  Many 

known  rings  have  reappeared  for  much  longer  periods  of  time 

250 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      251 

to  the  fact  that  the  underground  mycelium  either  exhausts  all 
available  food,  or  deposits  within  the  circle  secretions  which 
for  a  few  years  prevent  further  growth  of  this  fungus. 

Upon  logs,  trees,  and  stumps  many  kinds  of  toadstools 
are  found,  as  those  shown  in  Figs.  207  and  208.  But  most 
abundant  are  the  various  species  of  Polyporus  (meaning  many 
pores)  and  other  genera  (Fig.  209).  These  often  are  hard 


FIG.  207.  A  group  of  small  toad- 
stools (Marasmius)  growing  from 
decaying  wood 

Natural  size 


FIG.  208.   The  oyster  toadstool 
growing  upon  the  dead  and  de- 
caying branch  of  a  tree 

Three  eighths  natural  size 


and  woody,  and  instead  of  gills  they  have  many  small  pores 
upon  the  under  surface,  within  which  the  basidia  bear  the 
spores.  In  some  species  of  Polyporus  the  reproductive  body 
may  continue  its  growth  annually  for  many  years.  Meantime 
its  mycelium,  which  feeds  it,  has  been  growing  within  the 
tissues  of  the  host  and  gradually  bringing  about  its  decay. 
Another  toadstool  (Hydnum  septentrionale),  the  mycelium  of 
which  produces  the  heart  rot  of  the  sugar  maple,  forms  a 
reproductive  body  which,  though  its  general  form  is  like  the 


252 


PRACTICAL  BOTANY 


FIG.  209.  A  tree-destroying  fungus  (Polyporus  sulphureux)  growing  at  the 
base  of  a  red-oak  tree 

About  one  sixth  natural  size 


common  mushroom,  has  its  spores 
produced  upon  spines.  In  deep, 
moist  woods,  upon  old  logs,  a 
species  of  the  Hydnum  sometimes 
produces  an  immense  (twenty  to 
twenty-five  pounds)  edible,  coral- 
like,  reproductive  body.  A  coral- 
like  toadstool  is  Clavaria  (Fig. 
210). 

The  toadstools  and  mushrooms, 
both  saprophytic  and  parasitic,  are 
widely  distributed.  Forest  and  or- 
chard trees  are  in  great  danger 
of  infection  by  them  whenever 
open  wounds  are  left  from  broken 
limbs  or  pruning.  It  has  been 


FIG.  210.  A  coral-like  toadstool 

(Clavaria) 
One  half  natural  size 


THE  BASID1UM  FUNGI  (BASIDIOMYCETES)      253 


shown 1  that  a  single  Ayaricus  campestris  may  produce  not  less 
than  2,000,000,000  spores ;  that  the  "  shaggy-mane "  mush- 
room (Coprinus  comatus)  may  produce  5,000,000,000  spores; 
and  that  Polyporus  squamosus  may  produce  11,000,000,000 
spores.  It  is  also  inter- 
esting to  note  that  the 
same  authority  estimates 
that  in  Polyporus  squa- 
mosus one  spore  in  about 
1,000,000,000,000  has 
a  good  chance  to  start  a 
new  life  cycle. 

238.  The  puffballs. 
These  are  basidiomycetes 
whose  mycelium  usually 
grows  in  rich  soil,  and 
which  have  a  globular 
reproductive  body  that 
incloses  the  basidia  and 
spores.  Puffballs  may 
range  from  the  size  of  a 
pinhead  to  those  that  are 
a  foot  in  diameter  (Fig. 
211).  When  ripe  they 
burst  open,  usually  at 
the  top,  and  small  clouds 
of  spores  may  be  emitted 
at  intervals  for  months 
and  even  years.  The 
largest  known  puffball 
is  Lycoperdon  yiganteum.  One  specimen  of  it  which  measured 
sixteen  by  eleven  inches  was  estimated2  to  contain  7,000,000,- 
000,000  spores.  It  was  also  estimated  that  some  of  the  puffballs 

1  Buller,  A.  H.  R.,  Researches  on  Fungi.    Longmans,  Green,  and  Com- 
pany, 1909. 

2  Buller,  A.  II.  R.,  loc.  cit. 


FIG.  211.    Two  species  of  puffballs  of  the 
genus  Lycoperdon 

Those  above  are  one  half  natural  size,  and  that 
below  is  two  ninths  natural  size 


254 


PRACTICAL  BOTANY 


may  each  shed  spores  at  the  rate  of  1,000,000  per  minute, 
and  may  continue  this  for  several  days.  Another  puffball  is 
called  the  "  earthstar "  (  Geaster).  It  grows  in  sandy  and  waste 
places.  When  its  reproductive  body  is 
mature  the  outer  surface  peels  back  from 
the  tip,  thus  exposing  the  central  body, 
which  contains  the  spores.  A  closely 
related  form  is  the  stinkhorn  fungus 
(Fig.  212). 

The  nest  fungi  are  peculiar  puffballs 
which  grow  within  and  upon  rich  earth, 
well-decayed  wood,  old  manure  piles,  etc. 
The  reproductive  body  opens,  and  re- 
sembles a  small  cup  or  nest.  Within  the 
nest  are  a  few  egg-like  bodies  (Fig.  213), 
each  of  which  contains  a  mass  of  spores. 

239.  Summary  of  the 
fungi.  Because  of  their  ex- 
treme simplicity  and  their 
close  relation  to  the  blue- 
green  algse  the  bacteria  or 
schizomycetes  were  treated 
first  in  this  series  of  classes. 
Then  in  the  chapter  follow- 
ing the  algse  the  class  of 

fungi  called  phycomycetes,  FIG.  212.  The  stinkhorn  fungus  (Phallus) 
which  in  many  respects 
resemble  green  algse,  was 
discussed.  In  this  chapter 
classes  that  are  very  unlike 
algse — the  ascomycetes 
and  basidiomycetes  and  the 
lichens  —  are  discussed.  The  bacteria  are  so  simple  in  struc- 
ture that  they  are  generally  regarded  as  the  simplest  living 
organisms.  They  reproduce  themselves  almost  wholly  by  vege- 
tative processes,  occasionally  by  simple  resting  spores.  In  their 


At  its  spore-forming  period  this  has  a  very 
foul  odor,  that  attracts  flies,  which  are  said 
to  distribute  the  spores.  When  young  the 
whole  hody  is  a  whitish,  egg-shaped  mass. 
From  this  there  emerges  the  stalk,  upon  the 
end  of  which  is  the  spore-bearing  crown. 
One  half  natural  size 


THE  BASIDIUM  FUNGI  (BASIDIOMYCETES)      255 

life  processes  they  are  of  the  greatest  importance,  since  they 
are  instruments  of  decay  and  soil  enrichment,  and  bear  an  im- 
portant relation  to  various  industries.  As  producers  of  diseases 
of  plants,  animals,  and  men,  they  have  great  significance. 

Phycomycetes  are  sometimes  saprophytic  and  sometimes 
parasitic.  As  saprophytes  they  are  instruments  of  decay,  and 
as  parasites  they  often  kill  their  hosts  and  then  as  saprophytes 
disorganize  them.  The  simpler  phy corny cetes,  as  bread  mold, 


FIG.  213.  Nest  fungi  growing  in  soil  in  which  is  decaying  wood 

Within  the  cup-like  plants  are  the  egg-like  bodies  which  contain  the  spores. 

Natural  size 

reproduce  themselves  by  asexual  spores  and  by  forming  zygo- 
spores,  as  do  some  of  the  green  algse.  One  of  the  more  com- 
plex forms,  water  mold,  lives  in  the  water  and  reproduces  by 
means  of  zobspores ;  it  also  forms  oospores  by  means  of  special 
sex  organs.  Sometimes  its  oospores  are  produced  without  fer- 
tilization. Such  forms  as  the  downy  mildew  of  the  grape  are 
parasites.  They  bear  conidia,  or  sporangia-like  bodies,  upon  the 
leaves  of  their  hosts,  and  produce  oospores  within  these  leaves. 
Ascomycetes  have  conidia,  but  are  distinguished  by  the  fact 
that  some  of  their  spores  are  formed  in  sacs  at  the  tips  of 
hyphse.  These  sacs  are  in  open  cups,  as  in  Morchella,  Peziza, 
and  Sclerotinia ;  or  inclosed,  or  almost  so,  as  in  the  lilac  mil- 
dew. Some  forms  (^Penicillium  and  yeasts)  seem  to  have  lost 
part  of  the  usual  ascomycete  life  cycle.  The  life  habits  of 


256  PRACTICAL  BOTANY 

ascomycetes  are  of  great  importance  in  relation  to  dairy  indus- 
tries, fermentation,  and  to  diseases  of  economic  plants. 

Basidiomycetes  comprise  extremely  diversified  forms,  many 
of  which  (smuts  and  rusts)  are  not  conspicuous  except  in 
their  spore  formation.  Striking  polymorphic  life  cycles  are 
shown  in  the  rusts.  The  rusts  and  smuts  are  destructive  para- 
sites of  the  greatest  importance.  The  toadstools  and  mush- 
rooms, though  representing  a  very  large  number  of  forms  with 
world-wide  distribution,  have  a  comparatively  simple  life  cycle. 
They  are  chiefly  saprophytic,  though  several  forms,  as  the 
tree-destroying  fungi  and  others,  attack  living  hosts.  Puff- 
balls  are  almost  exclusively  soil  saprophytes. 

The  lichens  exhibit  a  remarkable  case  of  mutualism  or  of 
slavery  in  which  algae  and  fungi  live  together  in  such  a  way 
as  to  compose  a  new  organism.  In  these  organisms  the  algae 
do  the  necessary  chlorophyll  work,  and  the  fungi,  it  seems, 
protect  the  whole  organism,  thus  making  life  possible  in  places 
and  under  conditions  that  would  otherwise  be  impossible  for 
both  mutualists.  Algae  and  fungi  of  the  lichen  combination 
reproduce  themselves  in  the  ways  that  are  peculiar  to  the  algae 
and  fungi,  and  not  as  a  new  lichen  organism. 

240.  Classification 

Thallophytes 
Algae 
Fungi 

Class    I.    Phycomycetes 

Class  II.   Ascomycetes.  Leading  genera  used  as  illustrations,  — 

Peziza  (cup  fungus),  Sclerotinia  (brown  rot),  Microsphcera 

(lilac  mildew),  Morchella  (morel),  Penicilliinn  (blue  mold), 

Saccharomyces  (yeast),  Claviceps  (ergot),  etc. 

Class  III.    Lichens.    Leading  genera  used  as  illustrations,— 

Parmelia,  Usnea  (bearded  moss),  Cladonia,  etc. 
Class  IV.    Basidiomycetes.    Leading  genera  used  as  illustra- 
tions,—  Ustilayo  (smut),  Puccinia  (rust),   Uromyces  (rust), 
Gymnosporangium  (cedar  apple),  Agaricus,  Polyporus,  Hydnum 
(toadstools  or  mushrooms),  Lycoperdon  (puft'ball),  etc. 


CHAPTER  XVI 
MOSSES  AND  LIVERWORTS  (BRYOPHYTES) 

241.  Introductory  statement.  There  are  two  classes  of  this 
division  of  the  plant  kingdom,  —  the  mosses  (Musci)  and  liver- 
worts (Hepaticce).  The  name  Bryophytes  means  "  moss  plants." 
Liverwort  literally  means  "  liver  plant"  or  "  liver  root,"  so 
called  from  the  supposed  resemblances  in  form  between  the 
liverwort  plants  and  the  .human  liver.    There  is  a  rather  com- 
mon flowering  plant  (Ifepatica)  which   is   sometimes   called 
liverleaf  or  liverwort.   This  flowering  plant  should  not  be  con- 
fused with  the  true  liverworts.    Also  there  is  a  common  habit 
of  calling  all  small  green  plants  "mosses,"  but  when  we  dis- 
cover what  kind  of  plants  mosses  are,  we  shall  find  the  proper 
use  of  this  term. 

In  some  respects  liverworts  are  simpler  than  the  mosses, 
and  they  are  given  as  the  first  or  lowest  class.  But  it;is  so 
much  easier  to  get  clear  notions  of  some  aspects  of  bryophytes 
by  a  study  of  mosses  that  we  shall  first  consider  them. 

MOSSES 

242.  The  moss  plant:  the  protonema.    Mosses  of  various 
kinds  are  widely  distributed.    Careful  observation  of  a  moss 
plant  enables  one  to  see  that  it  has  green  leaf-like  structures 
arranged  around  a  very  small  stem.    Sometimes  also  there  ap- 
pears upon  this  leafy  stem  a  slender  stalk  with  a  swollen  pod- 
like  tip  or  capsule  (Fig.  216).    In  this  tip  are  many  simple 
asexual  spores,  and  we  shall  begin  the  life  cycle  by  following 
the  germination  of  one  of  them. 

When  an  asexual  spore  germinates  there  grows  from  it  a 
filamentous,  branching  body.  Its  cells  contain  chloroplastids 

257 


258 


PRACTICAL  BOTANY 


and  closely  resemble  cells  of  many  of  the  green  algse  (Fig. 
214,  A).  Mats  of  this  growth  form  upon  or  within  such  sub- 
stances as  soil,  logs,  etc.,  which  are  moist  and  shaded.  These 


FIG.  214.  The  moss  plant 

A,  the  alga-like  protonema  with  branches  (a) ;  a  young  bud  (c),  and  one  (6)  which 

has  divided  and  produced  several  cells.   -B,  a  bud  which  has  grown  until  young 

leaves  (c)  and  rhizoids  (6)  are  formed.    The  old  protonema  (a)  is  still  seen.   Both 

considerably  enlarged 

growths  are  so  alga-like  that  in  the  absence  of  considerable 
magnification  it  is  not  possible,  ordinarily,  to  distinguish  them 
from  the  algae.  At  times  some  of  the  cells  become  swollen, 


MOSSES  AND  LIVERWORTS  (BRYOPIIYTES)      259 

divide  by  oblique  walls,  and  form  buds  (Fig.  214,  A,  &).  These 
buds  continue  to  grow,  the  outermost  cells  develop  leaves,  the 
central  ones  become  the  stem,  and  from  the 
lower  ones  root-like  hairs  (ihizoids)  descend 
into  the  soil  (Fig.  214,  B,  6).  The  buds,  there- 
fore, are  the  beginnings  of  the  leafy  moss 
plant  (Figs.  215  and  216).  Young  buds  may 
grow  directly  into  leafy  plants,  or  become 
dormant  for  a  time  and  then 
resume  their  growth.  Since 
the  alga-like  growth  is  that 
which  precedes  and  produces 
the  leafy  moss  plant,  it  is 
called  the  protonema,  mean- 
ing "  primitive  thread." 

243.  The  moss  plant:  nu- 
trition. Dense  growths  of 
moss  plants  may  form  from 
a  single  mat  of  protonema. 
The  rhizoids,  embedded  in  soil,  humus,  or  de- 
caying timber,  bring  these  plants  into  close 
relation  with  the  water  supply.  The  whole 
dense  growth  may  serve  as  a  sponge,  so  that 
the  plants  may  then  be  virtually  immersed 
in  water.  Some  mosses  really  live  part  or 
all  of  the  time  in  streams  or  bodies  of  still 
water.  In  exposed  regions  mats  of  moss  may 
become  dry  enough  to  crumble  into  powder 
when  handled,  but,  if  undisturbed,  may  pro- 
ceed with  their  growth  upon  the  return  of 
moisture.  Some  mosses  also  show  remark- 
able ability  to  withstand  extremes  of  heat 
and  cold. 

The  stem  and  leaf  arrangement  that  exists  in  the  mosses 
exposes  chlorophyll  to  the  light  in  a  different  way  from  that 
which  was  found  in  the  algae.  With  the  leaves  arranged 


FIG.  215.  A  fully 

formed  leafy  moss 

plant 

Z,  leaves;  s,stem;  r, 

rhizoids.  Ten  times 

natural  size 


FIG.  216.  A  leafy 
moss  plant  upon 
which  the  sporo- 
phyte  has  grown 

Lp,  the  leafy  plant; 

s,  seta;  c,  capsule. 

Five  times  natural 

size 


260 


PRACTICAL  BOTAHY 


I  J 


radially  about  the  stem  much  more  chlorophyll  is  exposed  than 
could  be  exposed  in  the  same  space  by  a  prostrate  plant.   The 

importance  of  the  stem  in  holding 
these  leaves  up  into  the  air,  thus 
making  the  radial  arrangement 
possible,  is  evident.  It  is  also 
possible  that  no  less  importance 
should  be  attached  to  transpor- 
tation of  water  through  the  stem 
to  the  leaves,  though  it  is  not- 
known  to  what  extent  moss  leaves 
get  their  water  directly  through 
their  surfaces  or  through  the  stem. 
The  expanded  portions  of  the 
leaves  are  a  single  layer  of  cells  in 
thickness,  while  the  median  por- 
tion may  consist  of  several  layers 
of  cells.  In  the  middle  (midrib) 
there  are  rows  of  elongated  cells 
running  from  base  to  tip  of  the 
leaf.  These  constitute  the  vein  of 
the  leaf. 

244.  The  moss  plant :    sexual 
reproduction.    The  sex  organs  are 
borne  upon  the  upper  end  of  the 
stem.    If  the  terminal  leaves  are 
FIG.  217.  Archegonia  of  a  moss     carefully    removed    from    plants 

that  are  in  reproductive  condition, 
two  kinds  of  sex  organs  together 
with  some  sterile  filaments  (para- 
physes)  may  be  found.  In  some 
kinds  of  mosses  but  one  kind  of  sex 
organ  grows  upon  a  single  plant, 
while  in  other  kinds  both  may  grow 
upon  the  same  plant.  Magnifica- 
tion is  needed  in  studying  them. 


At  A  is  shown  the  tip  of  a  stem  of 
a  leafy  moss  plant,  with  the  frag- 
ments of  leaves  (T)  surrounding  a 
group  of  archegonia  (a).  At  B  is 
an  enlarged  archegonium,  in  the 
swollen  part  of  which  is  the  egg 
(e),  above  it  the  neck  (ri),  contain- 
ing the  neck  canal  cells,  and  at  the 
end  of  the  neck  are  the  cells  (m) 
which  later  open  to  form  the  place 
of  entrance  for  sperms.  A,  magni- 
fied 100  times;  B,  magnified  500 
times.  After  Sachs 


MOSSES  AND  LIVERWORTS  (BRYOPHYTES)      261 

One  of  the  sex  organs,  the  archegonium',  is  flask-like,  the  neck 
being  greatly  elongated  (Fig.  217,  A  and  B).  In  the  swollen 
part  of  the  archegonium  the  female  gamete  or  egg  is  formed. 
When  the  egg  is  mature  the  central  cells  in  the  neck  disor- 
ganize and  the  tip  of  the  neck  opens, 
thus  leaving  a,  gelatinous  passage- 
way into  the  open  end  of  the  arche- 
gonium and  through  the  neck  to 
the  egg.  The  other  sex  organ,  the 
antheridium,  is  club-shaped  (Fig. 
218),  being  attached  by  its  smaller 
end  to  the  end  of  the  stem.  Within 
each  antheridium  thousands  of  male 
gametes  or  sperm  cells  form.  When 
abundant  moisture  is  present  (dew 
or  rain)  the  antheridium  swells,  its 
tip  bursts  open,  and  the  contents 
escape.  The  biciliate  sperms  swim 
about  actively,  and  if  some  of  them 
come  into  the  vicinity  of  the  arche- 
gonium neck  they  make  their  way 
down  through  the  gelatinous  pas- 
sageway. One  of  the  sperms  unites 
with  the  egg,  thus  producing  the 
oospore.  It  is  evident  that  the  diffi- 
culty of  securing  fertilization  of  the 
egg  in  this  case  is  greater  than  in 
such  plants  as  VaucTieria  and  (Edogo- 
nium.  But  the  very  large  number  of 
sperms  produced  in  moss  antheridia 
helps  to  make  it  possible  for  sperms 
to  be  widely  spread,  thus  making  fertilization  more  probable. 

245.  The  moss  plant :  the  oospore  and  its  product.  The 
oospore  begins  to  grow  almost  as  soon  as  formed.  It  grows 
from  the  place  in  which  it  was  formed,  and  soon  elongates 
and  thickens  until  its  lower  end  pushs  down  into  the  end  of 


FIG. 218 

An  antheridium  (a)  of  a  moss. 
From  its  tip  the  sperms  (&)  are 
escaping,  and  one  of  them  is 
shown  enlarged  at  the  side  (c). 
a  and  6,  magnified  350  times; 
c,  magnified  800  times.  After 
Sachs 


262 


PKACTICAL  BOTANY 


the  stem  upon  which  the  archegonium  grew.    This  gives  the 
lower  end  a  foothold  in  the  stem,  and  by  reason  of  its  close 

contact  this  end,  or  foot  as  it  is 
called,  absorbs  food  material  from 
the  stem.  The  young  stalk  also 
bears  chlorophyll  and  may  manu- 
facture some  of  its  own  food.  The 
upward  end  elongates  rapidly  and 
carries  up  with  it  the  old  arche- 
gonium wall,  which  meantime  has 
grown  somewhat  (Figs.  216  and 
219).  This  elongated  structure 
is  called  the  seta,  which  means  a 
"bristle"  or  "hair."  Since  this  old 
archegonium  now  changed  is  like 
a  hood,  it  is  called  calyptra,  which 
means  "  hood."  Beneath  the  calyp- 
tra,  at  the  end  of  the  seta,  there 
is  formed  the  enlarged  capsule. 
Within  the  capsule,  by  division 
of  certain  specialized  cells,  large 
numbers  of  spores  are  formed.  At 
the  extreme  tip  of  the  capsule, 
beneath  the  calyptra,  is  the  mouth, 
oiperistome,  which  is  covered  by  a 
lid  known  as  the  operculum,  mean- 
ing the  "cover"  or  "lid."  When 
the  spores  are  ripe  the  calyptra 
may  fall  off  and  the  operculum  be 
thrown  off  by  swelling  of  the  cells 
immediately  below  it.  There  then 
appears  around  the  margin  of  the 
mouth  a  row  of  teeth  (Fig.  220). 
The  number  of  teeth  in  a  capsule 
is  definite  for  each  species  of  moss, 
and  sometimes  special  students  of 


FIG.  219.  Growth  of  the  moss 
oospore  to  form  the  sporophyte 

At  A  is  a  diagram  of  the  oospore 
after  it  has  gone  through  several 
cell  divisions  and  has  spread  the 
archegonium  wall.  B  shows  the 
tip  of  a  plant  stem  with  parts  of 
leaves  ahout.  The  oospore  has 
grown  into  a  stem-like  structure 
(«),  has  its  lower  end  inserted  in 
the  old  plant  stem  (gr),  and  the 
other  end  has  carried  up  the  en- 
larged archegonium  wall  (a)  as 
the  hood  or  calyptra.  After  Sachs 


MOSSES  AND  LJVEEWOKTS  (BRYOPHYTES)      263 


mosses  use  this  number  as  the  basis  of  distinguishing  one 
species  from  another.  On  account  of  the  regular  thickenings 
upon  the  teeth  they  are  readily  affected  by  moisture  changes ; 
that  is,  they  are  hygroscopic.  When  they  extend  within  the 
capsule  the  spores  adhere  to  them.  As  they  straighten  and 
extend  outward  they  move  with  a  jerking  motion  which  serves 
to  throw  the  spores  about.  A  moss  may  be  made  to  repeat  the 
characteristic  tooth  movements  under  a  hand  lens  or  low  power 
of  a  microscope,  by  being  moistened  and  then  fanned  until  dry. 

The  spores  developed  within  the 
capsules  are  made  entirely  by  cell 
division  and  are  therefore  asexual 
spores.    As  seen  in 
Section    242,    they  t 

may  germinate  and 
produce  protonema. 
Because  of  the  large 
number  and  wide 
distribution  of  asex- 
ual spores,  abun- 
dant production  of 
protonema  occurs 
when  the  favorable 
conditions  of  mois- 
ture, light,  and  tem- 
perature exist. 

246.  The  moss  plant :  alternate  stages  in  the  life  cycle.  It 
is  evident  that  in  the  mosses  sexual  and  asexual  reproduction 
are  limited,  each  to  a  distinct  part  of  the  life  cycle.  It  is  also 
evident  that  each  of  these  parts  of  the  life  cycle  forms  a  kind 
of  spore  which,  upon  germination,  produces  not  the  same  part 
of  the  life  cycle,  but  the  other  part.  The  asexual  spore  that  is 
formed  in  the  capsule  germinates  and  produces  protonema, 
which,  by  means  of  buds,  produces  the  leafy  plant;  the  oospore, 
which  is  produced  by  union  of  gametes, — the  egg  and  sperm, 
—  germinates  and  produces  the  foot,  seta,  and  capsule.  The 


FIG.  220.  Tips  of  moss  capsules 

A,  a  side  view  of  a  moss  capsule  showing  the  teeth  (t), 
and  the  mouth  or  peristome  (p),  to  which  the  teeth 
are  attached.  (Considerably  enlarged.)  B,  an  end 
view  of  a  moss  capsule.  Note  the  peculiar  spiral 
arrangement  of  the  teeth  and  the  transverse  thicken- 
ings upon  them.  (Greatly  enlarged) 


264 


PRACTICAL  BOTANY 


part  of  the  life  cycle  which  produces  the  asexual  spores  is 
called  the   sporophyte,  meaning  an   asexual  spore-producing 

plant.  The  part  which  pro- 
duces the  obspore  is  called 
the  gametopliyte,  the  gamete- 
producing  plant.  The  spo- 
rophyte, therefore,  is  the 
asexual  generation  of  moss, 
and  the  gametophyte  is  the 
sexual  generation.  The  rela- 
tion that  these  two  bear  to 
one  another  in  the  complete 
life  cycle  is  called  the  alter- 
nation of  generations. 

The  fact  that  the  proto- 
nema  and  leafy  shoot   are 
distinct  structures  does  not 
introduce   a   third   genera- 
tion, since  one 
of  those  struc- 
tures     grows 
from  the  other 
without  the  in- 
tervention   of 


FIG.  221.  Sphagnum 

A,  an  entire  plant  which  bears  capsules  upon  its  tallest  branch  (natural  size) ;  B,  two 
sporophyte  capsules  and  stalks  enlarged ;  C,  tip  of  a  vegetative  branch  enlarged 


MOSSES  AND  LIVERWORTS  (BRYOPHYTES)      265 

a  spore.  It  must  also  be  kept  in  mind  that  alternation  of 
generations  refers  to  alternation  between  the  sexual  genera- 
tion and  the  asexual  one.  In  case  of  several  kinds  of  asexual 
spore  reproduction,  such  as  were  seen  in  some  of  the  parasitic 
fungi,  the  term  alternation  of  generations  does  not  apply  in 
its  usual  meaning,  though  obviously  in  such  cases  there  is  a 
series  of  stages  that  make  up  the  life  round.  A  more  detailed 
discussion  than  we  have  given  might  show  a  real  alternation 
of  generations  in  algse  and  fungi,  but  for  an  elementary  study 
this  is  not  advisable." 

247.  Kinds  of  mosses.  There  are  hundreds  of  different 
species  of  mosses,  and  nearly  all  of  them  follow  closely  the 
life  cycle  already  outlined.  The  moss  used  for  the  illustra- 
tions (Figs.  215-220)  is  Funaria  hygrometrica.  Another  com- 
mon moss  and  one  of  the  larger  ones  is  pigeon-wheat  moss 
(Polytrichurni).  In  forests  it  commonly  produces  thick  cush- 
iony patches,  and  when  sporophytes  are  present  they  are  quite 
prominent  and  bear  unusually  large  calyptras. 

Peat-bog  moss  (Sphagnum)  is  a  very  striking  form,  which 
with  other  plants  may  form  peat.  It  is  common  in  bogs  every- 
where, and  grows  about  the  edge  of  the  water  or  upon  the 
extremely  wet  soil  that  has  been  formed  by  the  partial  decay 
of  plants.  Due  to  the  peculiar  structure  of  the  leaves  these 
plants  hold  water  in  great  quantities,  and  from  a  handful  of 
the  plants  water  may  be  pressed  as  from  a  wet  sponge.  The 
gametophyte  or  leafy  shoot  of  Sphagnum  continues  its  growth 
at  the  plant  tip  from  year  to  year,  and  the  older  buried  or 
submerged  portions  gradually  become  partially  decayed  and 
'intermingled  with  other  plant  material.  Dense  peat  masses 
are  thus  formed.  Such  material  forms  peat  fuel,  which  is  com- 
pressed, dried,  and  kept  for  sale  in  some  markets.  The  sporo- 
phyte  of  Sphagnum  is  quite  unlike  that  of  the  moss  described 
above,  since  it  is  merely  a  spherical  capsule  upheld  by  the  elon- 
gated stem  of  the  gametophyte  (Fig.  221).  Sphagnum  is  used 
quite  commonly  as  a  packing  material;  it  is  also  used  as  a 
covering  for  holding  moisture  within  the  soil  of  potted  plants. 


266 


PRACTICAL  BOTANY 


LIVERWORTS 

248.  Riccia.  Among  the  bryophytes  the  liverworts  are  sim- 
pler than  the  mosses,  and  some  of  the  liverworts  are  extremely 
simple.  Upon  moist  soil  at  the  margins  of  ponds  and  streams 
and  sometimes  free-floating  in  quiet  water,  the  small,  green, 
disk-like  Riccia  or  Ricciocarpus  plants  may  be  seen  (Fig.  222). 
Upon  careful  observation,  root-like  projections  (rhizoids)  may 
be  observed  upon  the  lower  surface.  The  plant  is  two-lobed, 
with  a  depression  or  notch  between  the 
lobes.  This  body  is  frequently  spoken 
of  as  a  thallus,  though  it  is  not  like  the 
thallophyte  body.  The  rhizoids  extend 
downward  and  backward  from  the  notch. 
The  upper  surface  of  Riccia  is  greener 
than  the  lower  surface.  Near  its  margin 
the  plant  may  be  but  one  or  a  few  layers 
of  cells  in  thickness.  Evidently  Riccia, 
though  a  prostrate  plant,  is  much  more 
complex  than  any  of  the  algae.  It  is  more 
complex  in  that  it  has  distinct  upper  and 
lower  surfaces,  with  root-like  hairs  grow- 
ing from  the  lower  surface.  It  is  also  to 
be  noted  that  it  has  a  distinct  apical  or 
growing  end  and  a  basal  end.  Chlorophyll 
is  borne  in  the  compact  body  cells,  and 
living  as  the  plant  does,  upon  damp  earth  or  in  water,  it  can 
readily  secure  the  materials  from  which  foods  are  manufactured 
It  is  more  complex  than  the  protonema  of  moss,  but  less  so 
than  the  leafy  shoot. 

In  reproducing  itself  each  individual  plant  of  Riccia  forms 
within  its  tissues  both  kinds  of  reproductive  organs.  One  of 
these  is  an  archegonium,  the  tip  of  which  just  reaches  the 
upper  surface  of  the  plant.  In  the  swollen  part  of  the  arche- 
gonium is  the  large  egg  cell,  which  is  therefore  deeply  em- 
bedded in  the  plant  tissues.  The  antheridia  also  open  to  the 


FIG.  222.  A  simple  liver- 
wort (Ricciocarpus) 

It  has  distinct  upper  and 
lower  surfaces,  bears  rhi- 
zoids (r)  on  the  under 
surface,  and  branches 
from  a  midrib  into  leaf- 
like  structures  (I) .  About 
five  times  natural  size 


MOSSES  AND  LIVER  WORTS  (BKYOPHYTES)      267 

upper  surface.  From  these  there  escape  large  numbers  of  cells, 
each  of  which  produces  a  sperm.  Sperms  enter  the  neck  of 
the  archegonium  and  one  unites  with  the  egg,  thus  producing 
an  oospore. 

The  oospore  does  not  grow  directly  into  a  new  plant,  but 
produces  an  enlarged  spherical  body  which  is  embedded  in  the 
tissues.  After  a  time  all  of  this  spherical  body  except  a  single 
layer  of  outside  cells  divides  into  spores.  These  escape  by  the 
breaking  down  of  the  tissues  of  old  plants.  They  may  grow 
into  new  Riccia  plants. 

The  main  Riccia  body  is  the  gametophyte,  since  it  produces 
the  gametes  which  form  the  oospore.  The  sporophyte  which 
develops  from  the  oospore  is  very  simple.  It  is  entirely  em- 
bedded within  the  gametophyte  body.  All  of  it  forms  spores 
except  a  single  outside  layer  of  cells.  Alternation  of  genera- 
tions is  as  truly  present  as  in  the  mosses  but  is  not  nearly  so 
conspicuous. 

249.  Marchantia:  vegetative  characteristics.  This  liverwort 
grows  in  moist  places,  such  as  swampy  regions,  shaded  river 
banks,  and  protected  rocky  ledges.  Sometimes  it  forms  exten- 
sive mats,  completely  covering  the  material  upon  which  it 
grows.  Single  plants  may  become  several  inches  in  length 
and  breadth  and  many  layers  of  cells  in  thickness.  Its  well- 
differentiated  upper  and  lower  surfaces,  apical  and  basal 
regions,  and  masses  of  rhizoids,  which  are  sometimes  an  inch 
or  two  in  length,  are  features  which  were  less  developed  in 
Riccia.  The  plants  grow  forward,  the  lobes  continuing  to 
branch,  until  at  times  quite  extensive  growths  are  produced 
(Fig.  223).  Older  portions  may  die,  leaving  the  younger 
branches  as  new  and  independent  plants. 

The  nutritive  tissues  of  Marchantia  are  highly  developed. 
There  are  chains  of  special  chlorophyll-bearing  cells  in  the 
upper  tissues.  These  semi-open  spaces  or  chambers  are  near 
the  upper  surface  of  the  plant.  The  surface  outline  of  these 
is  diamond-shaped.  Each  diamond-shaped  superficial  layer  of 
cells  has  in  its  center  a  chimney-like  pore  through  which  there 


268 


PRACTICAL  BOTANY 


is  atmospheric  contact  with  the  internal  chlorophyll  region. 
The  lower  layers  of  tissue  bear  less  chlorophyll,  but  they  com- 
pose the  main  supporting  part  of  the  plant.  From  these  the 
rhizoids  descend.  In  vegetative  structure  Marchantia  is  more 
complex  than  Riccia,  or  perhaps  than  mosses,  and  very  much 
more  complex  than  any  of  the  green  algae. 


FIG.  223.  A  common  liverwort  (Marchantia) 

The  plant  shown  at  the  left  is  an  archegonial  or  female  plant :  rh,  rhizoids ;  c,  cupules, 
in  which  are  buds  or  gemmae ;  s,  stalk  of  the  archegonial  branch ;  r,  radiating, 
finger-like  projections  of  the  head ;  a,  region  in  which  the  archegonia  are  borne. 
At  the  right  is  an  antheridial  plant :  a,  antheridial  head.  Both  plants  show  the  leaf- 
like  expansion  (I)  and  the  midrib  (m) .  About  one  and  one-half  times  natural  size 

250.  Marchantia:  vegetative  reproduction.  Upon  the  upper 
surface  of  Marchantia  in  the  midrib  region  there  are  frequently 
developed  cup-like  outgrowths  (cupules),  within  which  many 
buds  (gemmce)  are  formed  (Fig.  223,  <?).  The  gemmae  grow 
upon  small  stalks  from  the  bottom  of  the  cupules.  In  a  given 
cupule  there  may  be  gemmae  ranging  in  size  and  age  from 
those  that  consist  of  one  or  a  few  cells  to  those  with  dozens 


MOSSES  AND  LIVERWORTS  (BRYOPHYTES)      269 

of  cells.  These  older  mature  gemmee  are  flat,  and  have  two 
marginal  notches,  between  which  there  is  a  marginal  scar 
showing  where  the  gemma  was  attached  to  the  stalk  upon 
which  it  grew.  The  gemmae  may  grow  directly  into  new  Mar- 
chantia plants,  the  notches  being  the  points  at  which  growth 
begins.  Whichever  side  is  adjacent  to  the  earth  develops 
rhizoids  and  becomes  the  ventral  side,  while  the  other  becomes 
the  dorsal  side.  One  can  determine  which  side  of  a  gemma 
shall  develop  rhizoids  or  air  chambers  by  the  side  of  the 


FIG.  224.  Marchantia  antheridial  head,  antheridia,  and  sperms 

At  the  left  is  a  section  of  an  antheridial  head,  showing  several  antheridia  (a)  em- 
bedded near  the  surface.   At  the  right  is  shown  one  antheridium  in  detail,  and 
at  its  side  are  two  sperms  (*)  somewhat  enlarged.   After  Sachs 

gemma  which  is  placed  next  to  the  soil.  Even  after  growth  has 
begun,  if  the  gemmae  are  overturned,  the  development  from 
and  within  the  surface  tissues  will  change  to  that  which  is 
characteristic  of  lower  and  upper  surfaces  respectively.  Forma- 
tion of  gemmae  provides  Marchantia  with  a  ready  and  abun- 
dant method  of  vegetative  reproduction. 

251 .  Marchantia:  sexual  reproduction.  From  the  midrib  region 
of  the  flat  Marchantia  body  there  sometimes  grow  upright  stalks 
(Fig.  223).  The  tips  of  these  stalks  bear  heads  of  two  distinct 
kinds.  One  head  (antheridial)  is  flat  above  and  has  a  slightly 
indented  or  wrinkled  margin.  The  other  (archegonial)  is  more 
drooping  and  has  finger-like  rays  extending  from  its  main  body. 


270 


PRACTICAL  BOTANY 


Embedded  in  the  antheridial  head  are  the  antheridia  (Fig.  224), 
which  open  and  discharge  their  sperms  in  very  large  numbers 
upon  the  upper  surface.  The  archegonia  hang  downward  from 

the  underside  of  the  ar- 
chegonial  head  (Fig.  225). 
The  sperms  swim,  or  per- 
haps are  carried  by  contact 
with  bodies  of  small  ani- 
mals until  they  come  into 
the  vicinity  of  the  arche- 
gonia. They  enter  the  neck 
and  one  fertilizes  the  egg. 
The  oospore,  therefore,  is 
produced  in  the  archego- 
nium,  which  is  pendent 
from  the  underside  of  the 
archegonial  head. 

252.  Marchantia:  asex- 
ual reproduction.  The  oo- 
spore begins  to  grow  in 
the  position  in  which  it  is 
formed,  and  soon  produces 
an  oblong  body,  one  end 
of  which  is  the  foot  and 
the  other  the  capsule.  The 
foot  absorbs  nourishment 
from  the  archegonial  head 
at  the  old  archegonial  base. 
Within  the  capsule  many 
spores  are  produced  by  di- 
vision of  the  interior  capsule  tissues.  Also  some  of  these  inte- 
rior cells  form  elongated  spiral  threads,  which,  when  the  capsule 
bursts,  twist  and  squirm  about  as  they  dry  or  become  moist. 
This  twisting  motion  throws  the  spores  from  the  open  tip  of  the 
capsule.  These  spiral  filaments  which  assist  in  the  distribution 
of  spores  are  called  elaters,  meaning  "  drivers,"  or  "  hurlers." 


FIG.  225.  Part  of  an  archegonial  head  of 
Marchantia  in  diagram  so  as  to  show  the 
archegonia  (c)  hanging  down  from  the 
underside  of  the  head.  The  air  pores  (p), 
the  chlorophyll  cells  (chl),  and  the  loose 
tissue  (s)  which  surrounds  the  archegonia 

are  also  shown 
Modified  from  Bonnier  and  Sablon 


MOSSES  AND  LIVEEWOETS  (BEYOPHYTES)      271 


The  asexual  phase  or  sporophyte  of  Marchantia  is  not  conspic- 
uous, though  when  mature  it  sometimes  may  be  seen  without 
magnification.  It  is  evidently  a  little  more  complex  than  the 
corresponding  stage  in  Riccia.  This  asexual  generation  has  a 
foot  and  capsule,  while  in  Riccia  it  consisted  of  a  capsule  only. 
But  the  moss  sporophyte  is  much  more  complex  than  either, 
since  it  is  much  larger,  has  a  foot, 
seta,  and  very  complex  capsule, 
and  bears  chlorophyll  by  means  of 
which  it  may  do  photosynthesis. 


FIG.  226.  A  leafy  liverwort  (Frullania) 

At  A  is  a  plant  about  natural  size  as  it  appears  growing  upon  a  piece  of  maple 

bark  ;  at  B  is  an  enlarged  piece  of  the  same  plant,  showing  its  leaves,  rhizoids, 

and  the  peculiar  stalked  spore-capsule.   Modified  after  Kerner 

253.  Other  liverworts.  There  are  many  kinds  of  liverworts 
and  they ,  are  world-wide  in  distribution.  They  are  usually 
found  in  damp  and  shady  places.  A  few  species  live  in  the 
water.  In  the  moist  tropics  they  may  be  found  upon  the 
trunks  or  even  the  leaves  of  trees. 

The  liverworts  may  have  flat  dorsiventral  bodies,  such  as 
were  seen  in  Riccia  and  Marchantia,  or  they  may  be  differen- 
tiated into  stem  and  leaf-like  organs  (Fig.  226),  with  the  rhi- 
zoids at  or  near  the  basal  end  of  the  plants.  It  is  sometimes 
difficult  for  any  one  except  a  specialist  to  distinguish  some  of 


272 


PRACTICAL  BOTANY 


the  leafy  liverworts  from  some  of  the  mosses  except  when  the 
sporophytes  are  present.  In  one  group  of  liverworts,  of  which 
the  horned  liverwort  (^AntTioceros)  is  the  commonest  represent- 
ative, the  gametophyte  is  strikingly  simple  and  the  sporophyte 
equally  striking  in  its  complexity  (Fig.  227).  This  plant  is 
widely  distributed  upon  damp  rocks,  banks  of  streams,  and  often 
in  open  meadows.  The  gametophyte  is  small  and  extremely 

thin.  The  simple  antheridia 
and  archegonia  are  embedded 
in  the  gametophyte.  After  the 
oospore  is  formed,  it  germi- 
nates and  produces  a  sporo- 
phyte, which  consists  of  a 
large  swollen  foot  region  and 
prominent  stalk.  The  foot  is 
well  fitted  to  absorb  nourish- 
ment from  the  gametophyte 
and  the  stalk  bears  chlorophyll. 
The  presence  of  stomata  in  the 
stalk  further  suggests  ability 
to  do  chlorophyll  work.  In- 
deed, if  the  sporophyte  could 
live  with  its  foot  in  the  soil, 
it  might  live  independent  of 
the  gametophyte.  The  entire 
stalk  becomes  a  kind  of  cap- 
sule, part  of  its  tissues  forming 
spores,  first  at  its  tip,  then  lower  and  lower  down  to  the  base. 
It  is  the  supposed  resemblance  of  the  sporophyte  to  a  horn 
which  gave  the  name  horned  liverworts  to  the  Anthoceros  forms, 
254.  Summary  of  the  bryophytes.  The  bryophytes  are  in 
many  respects  higher  plants  than  the  thallophytes.  Sexual 
reproduction  by  means  of  complex  archegonia  and  anther- 
idia occurs  upon  one  phase  of  these  plants,  and  asexual 
reproduction  by  means  of  special  capsules  occurs  upon  a  dis- 
tinctly different  part  of  the  plant's  life  cycle.  This  constitutes 


--9 


r 


FIG.  227.  Anthoceros,  a  liverwort 
with  very  simple  thallus  and  com- 
plex sporophyte 


MOSSES  AND  LIVEKWOETS  (BRYOPHYTES)      273 

alternation  of  generations.  In  the  mosses  the  two  generations 
are  easily  observed.  There  is  a  gradual  development  of  the 
sporophyte  from  the  very  simple  condition  in  Riccia  through 
many  intermediate  forms,  one  of  which  is  Marchantia,  to  the 
relatively  complex  condition  in  Antlioceros.  From  an  entirely 
dependent  sporophyte  which  is  embedded  within  the  tissues  of 
the  gametophyte,  such  as  is  seen  in  Riccia,  there  is  an  increase 
in  complexity  of  the  sporophyte  until  it  becomes  an  upright, 
chlorophyll-bearing,  almost  independent  structure.  Although 
almost  all  of  the  Riccia  sporophyte  produces  spores,  the  cap- 
sule is  so  small  that  the  total  number  of  these  spores  is  not 
large.  As  the  sporophyte  increases  in  size  and  becomes  more 
specialized,  proportionately  less  of  it  is  devoted  to  spore  pro- 
duction, but  actually  very  many  more  spores  are  formed,  since 
the  whole  spore-producing  part  of  the  sporophyte  is  so  large. 
The  gametophyte  is  the  chief  chlorophyll-working  generation 
in  bryophytes,  and  the  sporophyte  depends  upon  it  for  all  or 
most  of  its  nourishment.  Special  structures  for  the  perform- 
ance of  nutritive  work  by  the  gametophytes  exist.  These  are 
rhizoids,  leaves,  and  stems.  It  is  worthy  of  note  that  in  none 
of  the  succeeding  groups  of  plants  is  the  gametophyte  so  well 
equipped  for  independent  nutritive  work  as  in  the  bryophytes. 

255.  Classification: 

Bryophytes 

Class  I.  Hepaticae  (liverworts).   Leading  genera  used  as  illustrations, 

—  Riccia,  Marchantia,  Antlioceros 

Class  II.    Musci  (mosses).    Leading  genera  used  as  illustrations, — 
Funaria,  Sphagnum,  Polytrichum 


CHAPTER  XVII 
THE  PTERIDOPHYTES 

256.  Introductory  statement.  This  division  of  the  plant 
kingdom  is  usually  spoken  of  as  the  ferns.  It  must  be  under- 
stood at  the  beginning  of  the  study,  however,  that  the  true 
ferns  constitute  but  one  class  of  pteridophytes.  Two  other 
classes  are  the  scouring  rushes,  or  horsetails,  and  the  club 
mosses.  There  are  other  classes  of  pteridophytes,  but  since 
they  are  represented  by  only  a  few  highly  specialized  plants, 
and  since  these  are  not  often  observed  by  general  students, 
they  are  not  of  great  importance  in  an  elementary  treatise. 
There  is  abundant  evidence  that  ferns  were  formerly  more 
numerous  upon  the  earth,  and  some  of  them  of  much  larger 
size  than  those  that  now  exist.  Some  of  these  ancient  forms 
doubtless  represented  classes  that  are  now  extinct,  and  others 
were  the  older  members  or  the  ancestors  of  the  classes  which 
we  now  have,  and  which  in  some  cases  are  now  represented 
by  only  a  few  kinds  of  plants. 

THE  TRUE  FERNS  (FILICINE^) 

Those  plants  which  are  ordinarily  regarded  as  ferns  belong 
to  this  class.  They  may  grow  in  almost  any  region  where  any 
plants  are  found.  Most  ferns  grow  in  moist  regions,  but  some 
species  occur  in  peculiarly  dry  situations.  Although  they  show 
considerable  variation  in  form,  they  can,  in  nearly  all  cases, 
be  distinguished  from  other  plants  by  their  greatly  divided, 
feather-like  leaves  (Fig.  228).  There  is  much  range  in  size  of 
ferns,  from  very  small,  lowly  plants  to  those  as  high  as  a  man's 
head,  and  to  tree  ferns  that  may  be  forty  feet  or  more  in  height 
(Fig.  229).  In  some  regions  dense  thickets  of  ferns  are  formed. 

274 


FIG.  228.  The  bracken  fern  (Pteris  aquilina) 

The  rootstock  (rh)  is  horizontal  and  grows  underground ;  upon  it  are  the  buds  (6) 

and  the  upright  leafstalk  (sf) 

275 


276 


PRACTICAL  BOTANY 


In  all  except  the  tree  ferns,  the  parts  of  the  plants  that  we 
see  are  the  leaves,  the  stems  and  roots  being  underground. 
We  shall  understand  the  fern  class  as  a  whole  better  if  we 
study  one  plant  in  detail,  and  then  consider  other  forms. 


FIG.  229.  Tree  ferns  (Alsophila)  upon  the  bank  of  a  stream  in  Mexico 
The  larger  plant  is  almost  40  feet  in  height.  Photograph  by  W.  J.  G.  Land 

257.  A  fern  plant:  the  rootstock  (rhizome).  If  we  carefully 
remove  the  soil  from  the  underground  part  of  one  of  the  com- 
mon ferns,  we  shall  find  the  horizontal  rootstock  (rhizome) 


THE  PTERIDOPHYTES 


277 


(Fig.  228).  The  lower  side  of  the  rhizome  gives  rise  to  the 
roots,  and  the  upper  side  bears  the  leaves.  At  the  tip  of  the 
rootstock  is  the  bud,  by  means  of  which  growth  is  contin- 
ued from  year  to  year.  By  carefully  studying  the  leaf  scars 
or  the  bases  of  old  leaves  upon  the  rootstock,  it  is  usually 


„, 


FIG.  230.  Diagram  of  a  cross  section  of  the  underground  stem  of  a  fern 

The  outer  part  of  the  stem  is  made  up  of  hard  tissue  and  in  the  interior  are  also 

bundles  of  hard  tissue  (s)  known  as  sclerenchyma ;  numerous  woody  bundles  (f.b) 

are  also  surrounded  by  the  large  amount  of  pith 

possible  to  determine  the  age  of  the  latter,  - —  that  is,  the  age  of 
this  particular  fern  plant.  The  terminal  bud  grows  forward 
each  year  from  a  fraction  of  an  inch  in  some  ferns  to  several 
inches  in  others,  and  at  the  beginning  of  each  season  it  sends 
up  one  or  a  few  new  leaves. 

The  rhizome  of  the  fern  presents  the  first  really  complex 
stem  structure  that  we  find  as  we  study  the  groups  of  plants 


278  PRACTICAL  BOTANY 

in  the  order  of  their  increasing  complexity.  This  is  a  woody 
stem  composed  of  several  kinds  of  stem  tissues.  Some  of  these 
tissues  are  very  heavy-walled  and  give  rigidity  to  the  stem. 
The  heavy-walled  cells  (sclerenchyma)  may  be  around  the 
outside  as  well  as  within  the  stem  (Fig.  230).  Other  tissues 
are  composed  of  large  pithy  cells  with  thin  walls  (parenchyma). 
These  cells  are  sometimes  stored  full  of  food  in  the  form  of 
starch.  Still  other  tissues  consist  chiefly  of  rounded,  fiber-like 
bundles  which  extend  lengthwise  throughout  the  stem.  These 
are  the  fibrovascular  bundles,  which  means  "  fibrous  bundles  of 
vessels."  A  careful  inspection  of  one  of  these  bundles  discloses 
two  kinds  of  tissues  composing  it,  —  one  usually  of  large  cells 
with  hard,  heavy  walls  (the  xylem),  and  the  other  with  thin- 
walled  cells  (the  phloem).  It  is  customary  to  speak  of  the 
xylem  bundle  and  the  phloem  bundle,  in  which  case  we  should 
have  in  the  fern  a  compound  bundle,  the  phloem  being  ar- 
ranged concentrically  about  the  xylem.  About  these  is  a  layer 
of  cells  known  as  the  endodermis,  meaning  "  inside  epidermis." 
The  fibrovascular  bundles  are  special  conducting  tissues. 
Through  these  water  and  materials  in  solution  in  it  are  carried 
to  the  leaf,  and  manufactured  foods  are  carried  back  to  stem 
and  roots.  It  is  thought  that  the  water  is  carried  upward 
chiefly  through  the  xylem,  and  that  manufactured  food  is 
carried  downward  through  the  phloem.  The  fibrovascular 
bundles  extend  throughout  the  roots  and  leaves. 

258.  The  fern  plant :  the  leaf.  By  means  of  a  transverse 
section  of  the  leafstalk  it  is  seen  that  conducting  bundles  and 
sclerenchyma  are  present  as  in  the  rhizome,  though  the  arrange- 
ment differs  in  some  ways.  The  hard  surface  of  the  leafstalk 
is  due  to  the  presence  of  sclerenchyma,  and  its  strength  par- 
tially to  sclerenchyma  and  partially  to  fibrovascular  bundles. 
The  fibrovascular  bundles  extend  by  branches  into  the  green 
leaflets,  where  they  are  recognized  as  the  veins  of  the  leaf. 

By  removing  the  leaf  surface  (epidermis)  and  examining 
with  a  microscope  its  structure  may  be  seen.  It  consists  of  a 
single  layer  of  cells  whose  irregular  walls  fit  into  one  another 


THE  PTEKIDOPHYTES  279 

quite  closely.  In  the  lower  epidermis,  rarely  in  the  upper,  are 
the  stomata.  By  means  of  a  transverse  section  of  a  leaflet 
(Fig.  231)  the  other  leaf  tissues  are  seen  to  be  (1)  the  veins, 
which  appear  in  cross  section  as  bundles  of  very  small,  heavy- 
walled  cells ;  and  (2)  the  chlorophyll-bearing  cells.  The  upper- 
most chlorophyll-bearing  cells  are  long  and  stand  close  together 
(palisade  tissue),  with  then-  ends  at  right  angles  to  the  sur- 
face. The  other  chlorophyll-bearing  cells  are  loosely  arranged, 
(the  spongy  tissue)  and  between  them  are  many  air  spaces. 


FIG.  231.  A  cross  section  of  part  of  a  fern  leaf,  showing  the  indusium  (i) 
and  sporangia  (s)  on  the  underside 

After  Engler  and  Prantl 

259.  Importance  of  introduction  of  fibrovascular  tissue.  It 
is  evident  that  a  fern  leaf  exposes  much  chlorophyll  to  the 
light,  —  much  more  than  did  any  plant  among  the  bryophytes. 
The  strong  supporting  and  conducting  tissues  of  the  leaf 
uphold  the  chlorophyll  tissues  in  such  a  position  that  they 
may  receive  light;  at  the  same  time,  through  the  fibrovascular 
bundles  of  the  leaf,  soil  water  may  be  transported  up  to  the 
chlorophyll  tissue.  The  root  system  anchors  the  plant  in  the 
earth  and  absorbs  the  water  needed  in  food  manufacture. 


280 


PRACTICAL  BOTANY 


In  general,  plants  which  rise  above  the  soil  and  into  the  air 
must  be  supported,  and  must  secure  water  from  some  source. 

The  climbing  vines 
which  are  dependent 
upon  other  plants  are 
supported  by  plant 
tissue,  though  it  is 
not  their  own.  Most 
vines  procure  their 
supply  of  water  from 
the  soil  and  transport 
it  by  means  of  their 
own  vascular  tissues. 
Fibrovascular  tissue 
makes  possible  the 
upright  position  and 
is  essential,  as  is  also 
the  absorbent  and  an- 
choring root  system, 
alike  to  the  fields  of 
upright  grain  and  to 
the  forests. 

260.  The  fern  plant: 
asexual  reproduction. 
On  the  undersides  of 
the  fronds  or  leaves 
of  most  common  ferns 
there  may  at  times  be 
found  small  brown- 
ish dots  (sori)  com- 
posed  of    sporangia. 
These  dots  may  each 
FIG.  232.  Leaflets  from  four  kinds  of  ferns          be  covered  by  a  shield- 
In  the  different  specimens  the  sporangia  are  at  a,       ^6  Outgrowth  from 
the  indusium  at  *,  and  the  false  indusium  at/.t.       t}le     epidermis     (the 
A,  bracken  fern;  B,  shield  fern;   C,  spleenwort;        .  ,r  v 

and  D,  the  maidenhair  fern  indusiuni)  (Fig.  231), 


THE  PTERIDOPHYTES  281 

or  by  the  recurved  leaf  margin,  which  is  known  as  a  false  indu- 
sium  (Fig.  232).  Each  species  of  fern  has  a  regular  position 
in  which  its  sori  appear,  and  in  some  cases  their  arrangement 
and  relation  to  the  veins  are  used  in  distinguishing  species 
from  one  another. 

In  most  of  the  common,  ferns  the  sporangia  are  of  the 
form  shown  in  Fig.  233.  Each  consists  of  a  stalk,  at  the  free 
end  of  which  is  a  flattened  capsule.  Within  the  capsule,  by 
division  of  the  tissues,  numerous  asexual  spores  are  formed,, 


FIG.  233.  A  fern  sporangium,  showing  its  behavior  in  the  process  of 

distributing  its  spores 
Much  magnified.   After  Atkinson 

The  capsule  wall  is  extremely  thin  and  consists  of  a  single  layer 
of  cells.  From  the  end  of  the  sporangium  stalk  over  the  cap- 
sule, and  halfway  to  the  stalk  again,  is  a  row  or  ring  (annulus) 
of  cells,  which  have  heavy  walls  on  all  but  the  outer  side. 
At  the  tip  of  the  annulus  is  the  capsule  mouth,  about  which 
are  two  pairs  of  specially  formed  cells  known  as  the  lip  cells. 
When  the  spores  within  the  capsule  are  ripe,  the  indusium 
becomes  dry  and  turns  up  sufficiently  to  expose  the  sporangia. 
The  annulus  upon  a  ripe  capsule  then  begins  to  dry.  Its  outer 
wall,  being  thin,  permits  its  cells  to  contract  as  the  whole 


282 


PRACTICAL  BOTANY 


annulus  opens  outward.  The  capsule  is  torn  open  at  the  mouth, 
and  its  entire  upper  half  may  thus  be  turned  back  with  the 
annulus ;  this  occurs  so  slowly  that  part  or  all  of  the  spores 
within  the  upper  part  of  the  sporangium  may  be  carried  back 
within  it.  The  annulus  becomes  tense,  like  a  tightly  drawn 

elastic  spring, — 
then  flies  again 
into  its  original 
position,  and  in 
so  doing  throws 
spores  with  con- 
siderable force. 
By  mounting  spo- 
rangia under  a 
low-power  micro- 
scope, moistening 
them,  and  then 
watching  them 
as  they  become 
dry,  their  action 
will  be  seen ;  but 
the  closing  of  the 
sporangia  often 
happens  so  sud- 
denly as  to  elude 
FIG.  234.  Development  of  the  fern  gametophyte 

the  careless  ob- 

A,  an  asexual  spore ;  B  and  C,  asexual  spores  germinat- 
ing, each  having  produced  a  green  filament  and  a  rhizoid ; 
D,  the  broadening  of  the  green  filament  and  the  differ- 
entiation of  an  apical  cell  (a) ;  E,  a  well-formed  fern 
gametophyte ;  D  and  E  are  diagrams  and  E  is  made  on 
a  much  smaller  scale  than  the  others.  All  considerably 
enlarged 


server,  and  the 
spores  are  usu- 
ally thrown  so 
far  that  they  are 


altogether  lost. 

Since  these  spores  are  formed  within  a  capsule  by  division  of 
the  tissues,  it  is  clear  that  they  are  asexual  spores.  The  com- 
plex leafy  fern  plant  is  the  sporophyte,  since  it  forms  asexual 
spores.  It  produces  these  in  very  large  numbers,  thus  providing 
abundantly  for  possibilities  of  gametophyte  production. 


THE  PTEKIDOPHYTES 


283 


261.  The  fern  plant :  the  gametophyte  and  sexual  reproduc- 
tion. Upon  moist  earth,  pots  in  greenhouses,  etc.,  the  asexual 
fern  spores  germinate.    First  a  stout  green  cell  is  produced, 
and  at  its  base  there  appears  a  hair-like  cell,  the  first  rhizoid 
(Fig.  234,  B  and  (7).    The  green  cell  grows  rapidly  and  soon 
divides  to  form  a  row  of  cells  (Fig.  234,  D). 

Thereafter  the  tip,  by  means  of  a  special  apical  cell,  expands 
into  a  broad,  heart-shaped  plant  (Figs.  234,  E,  and  235,  A). 
At  the  margin  this  plant  is 
one  layer  of  cells  in  thick- 
ness, but  along  the  midrib 
quite  a  cushion  of  cells  is 
formed.  From  the  under- 
side and  near  the  base  many 
rhizoids  grow.  The  presence 
of  chlorophyll,  and  contact 
with  moist  surfaces  neces- 
sary for  water  supply,  aid 
the  gametophyte  in  manu- 
facturing its  own  food. 

262.  The  fern  plant:  sex- 
ual reproduction.  Antheridia 
may  be  developed  upon  the 
filamentous  green  cells  be- 
fore the  heart-shaped  gametophyte  is  formed,  or  upon  the  older 
gametophyte  they  may  develop  toward  the  basal  region  and 
on  the  underside  (Fig.  235).    The  antheridium  is  a  globular 
structure  with  a  single  layer  of  wall  cells  (Fig.  236,  A),  and  a 
central  cell  in  which  usually  thirty-two  or  sixty-four  sperms 
are  formed.    In  size  and  number  of  cells  this  antheridium  is 
much  simpler  than  that  seen  in  bryophytes.  The  sperm  is,  how- 
ever, quite  complex  and  seems  well  constructed  for  swimming 
(Fig.  236,  B). 

Also  on  the  underside  of  the  gametophyte  and  nearer  the 
apical  region  are  the  archegonia  (Fig.  235).  Only  the  necks 
extend  out  from  the  surface,  and  these  usually  turn  backward 


FIG.  235.  J.,  a  diagram  of  the  underside 
of  a  fully  formed  fern  gametophyte, 
showing  rhizoids,  antheridia,  and  ar- 
chegonia ;  #,  a  fern  gametophyte  from 
which  a  young  sporophyte  is  growing 

Both  somewhat  enlarged 


284 


PRACTICAL  BOTANY 


toward  the  antheridia.  The  enlarged  part  of  the  archegonium, 
where  the  egg  is  formed,  is  embedded  in  the  tissue  of  the  ga- 

metophyte.  The  neck 
opens  (Fig.  237), 
sperms  enter,  and 
one  of  them  unites 
with  the  egg.  The 
resulting  oospore  is 
consequently  formed 
within  the  gameto- 
phyte  tissue. 

263.  The  fern  plant: 
the  young  sporophyte. 
The  oospore  begins 
its  growth  while  still 
within  the  gameto- 
phyte.  It  soon  pro- 
duces a  foot,  which 
absorbs  nourishment 
out  of  the  gameto- 
phyte.  It  also  pro- 
duces a  root,  stem, 
and  leaf,  and  these 
beginnings  of  the 
leafy  plant  are  called 
the  sporophyte  em- 
bryo. In  most  ferns 
the  embryo  root  soon 
dies  and  the  stem 
becomes  a  prostrate 
underground  root- 
stock  from  which  the 
new  roots  grow.  The 
leaf  arises  into  the 
air  and  the  new  sporophyte  is  thus  established  (Fig.  235,  J5) 
as  the  chlorophyll-working  fern  of  our  common  observation. 


FIG.  236.  Fern  antheridium  and  sperms 

A,  an  antheridium  from  which  the  sperms  are  escap- 
ing ;  JB,  one  enlarged  sperm.  All  greatly  magnified. 
After  Luerssen 


THE  PTERIDOPHYTES 


285 


\ 


264.  The  fern  plant :  gametophyte  and  sporophyte.    Each 

generation  of  the  fern  produces  chlorophyll  and  can  manufac- 
ture its  own  food  material.  In  a  sense  each  is  an  independent 
plant,  but  the  gametophyte  is  too  delicate  to  undergo  severe 
climatic  conditions.  It  resembles  some  of  the  liverworts,  but 
its  sexual  reproductive  structures  are  different.  The  embryo 
sporophyte  that 
begins  to  grow 
within  the  game- 
tophyte is  com- 
plex, consisting 
of  foot,  primary 
root,  stem,  and 
leaf,  though  but 
two  of  these  per- 
sist in  the  adult 
sporophyte. 

This  embryo 
begins  its  life 
entirely  inside 
of  the  gameto- 
phyte, but  soon 
emerges  and  be- 
comes a  sporo- 
phyte plantlet. 

It  should  also  be  noted  that  in  ferns  there  is  a  great  reduc- 
tion in  the  number  of  sperms  produced  in  an  antheridium  as 
compared  with  bryophytes,  but  each  sperm  is  more  complex. 
Reduction  in  number  seems  to  be  balanced  by  the  increased 
efficiency  of  those  that  are  formed. 

The  sporophyte  is  the  prominent  fern  plant  and  the  chief 
chlorophyll-working  generation.  It  introduces  new  sporophyte 
structures  and  habits,  supporting  and  conducting  tissues,  and 
the  upright  habit.  This  condition  was  forecasted  in  the  sporo- 
phyte of  Anthoceros,  but  fern  sporophytes  are  very  much  more 
complex  than  those  of  Anthoceros.  Though  many  asexual 


FIG.  237.  A  fern  archegonium 

In  the  neck  are  the  neck-canal  cells,  and  at  the  base  of  the 
neck  is  the  egg.   Greatly  magnified 


286 


PRACTICAL  BOTANY 


FIG.  238.  The  bulblet  fern  (Cystopteris  bulbifera) 

A,  a  leaf  upon  which  vegetative  reproductive  growths 

or  bulbs  (6)  are  formed ;  B,  a  section  of  the  leaf  on 

the  underside  of  which  groups  of  sporangia  (indusia) 

are  borne ;  C,  one  indusium  in  detail 


spores  are  produced,  a  com- 
paratively small  part  of  the 
sporophyte  is  given  to  spore 
formation,  most  of  it  doing 
nutritive  work.  The  fern 
sporophyte  may  grow  from 
year  to  year  (is  perennial), 
producing  new  leaves,  a  new 
supply  of  food,  and  new  crops 
of  spores  each  year. 

The  complexity  and  prom- 
inence of  the  fern  sporo- 
phyte and  the  comparative 
simplicity  and  inconspicu- 
ousness  of  the  gametophyte 
are  forerunners  of  the  greater 
increase  in  sporophyte  and 
decrease  in  gametophyte 
that  is  to  be  found  later  in 
higher  plants. 

265.  Types  of  ferns. 
Ferns  are  usually 
distinguished  from 
one  another  by  the 
leaves,  the  sori,  and 
the  sporangia.  There 
is  considerable  varia- 
tion in  position  and 
arrangement  of  sori 
in  different  ferns 
(Figs.  232,238,239), 
In  some  the  sori  are 
regularly  placed  dots 
upon  the  leaf.  In 
others,  as  the  maiden- 
hair fern  (Adiantum) 


FIG.  239.  At  the  left  is  the  "interrupted  fern,"  or  Clayton's  fern  (Osmunda 
Claytoniana),  in  which  sporangium-bearing  leaflets  (sp)  are  distinct  and  inter- 
mediate with  foliage  leaflets.  At  the  right  is  the  royal  fern  (Osmunda  regalis) 

A,  a  leaf  with  sporangium-bearing  leaflets  at  its  tip.  Z?,  (7,  D,  stages  in  the  devel- 
opment of  sporangium-bearing  leaflets  from  foliage  leaflets.  Both  about  one 

third  natural  size 

287 


FIG.  240.  The  Virginia  grape  fern  (Botrychium  virginianum) 

The  spore-bearing  part  of  the  leaf,  sporophyll  (s.l),  is  differentiated  from  the 
foliage  part  of  the  leaf  (/./).  One  fourth  natural  size 


288 


FIG.  241.  The  sensitive,  or  oak  fern  (Onoclea  sensibilis) 

r.s,  rootstock  or  rhizome ;  Ls,  leaf  bases  of  former  years ;  f.l,  foliage  leaf  • 
s.l,  sporangium-bearing  leaf.   One  fourth  natural  size 

289 


290 


PRACTICAL  BOTANY 


and  the  bracken  fern  (Pteris  aquilina),  and  other  species  of 
Pteris,  the  sporangia  are  covered  by  the  folded  leaf  margins. 
In  the  walking  fern  (Camptosorus  rhizophyllus)  sori  are  in 

long  slits  arranged  diag- 
onally to  the  midrib. 

In  the  royal  fern 
(Osmunda  regalis)  (Fig. 
239)  sporangia  are  borne 
only  upon  tip  leaflets. 
Such  leaflets  usually  bear 
dense  masses  of  sporan- 
gia and  do  little  or  no 
chlorophyll  work.  Often, 
however,  one  may  see 
a  single  plant  exhibit- 
ing the  following  grada- 
tion in  the  development 
of  sporangium-bearing 
leaflets :  (1)  chlorophyll 
leaflets;  (2)  chlorophyll 
leaflets  with  one  margin 
bearing  a  few  sporangia ; 
(3)  one  entire  side  of 
a  leaflet  bearing  sporan- 
gia ;  (4)  the  entire  leaflet 
bearing  sporangia  (Fig. 
239,  B,  C,  D). 


FIG.  242.  A  water  fern  (Marsilia) 


The  rootstock  (st),  with  the  descending  roots 
(r) ,  grows  in  the  soil  at  the  bottom  of  shallow 
pools  of  standing  water.  From  the  rootstock 
the  leaves  (I,  I',  and  I")  arise.  The  expanded 
part  of  the  leaf  may  float  upon  the  surface  of 
the  water,  or  at  times  may  stand  ahove  the 
water.  Special  spore-bearing  cases  (s)  are  borne 
upon  short  branches  from  the  leafstalk 


In  Clayton's  fern,  or 
the  "  interrupted  "  fern 
(^Osmunda  Olaytoniana) 
(Fig.  239),  a  group  of 
intermediate  leaflets  are  entirely  sporangium-bearing.  In  the 
Virginia  grape  fern  (Botrychium  virginianum)  (Fig.  240) 
the  leaf  is  differentiated  into  a  spore-bearing  branch  and  a 
three-parted  chlorophyll  branch.  In  such  cases  the  former  is 
called  the  sporophyll,  meaning  "  spore  leaf,"  and  the  latter  the 


THE  PTERIDOPHYTES 


291 


foliage  leaf.    In  the  sensitive  fern  (Fig.  241)  and  ostrich  fern 

and  some   others  the  sporophyll   and  foliage  branches  rise 

separately  from  the  rhizome.    This  division  of  labor  in  fern 

leaves,  resulting  in  development 

of  distinct  sporophylls  and  foliage 

leaves,  is  a  great  advance.  Setting 

apart  special  structures  for  special 

pieces  of  work  (division  of  labor) 

ordinarily  increases   the  quality 

and  quantity  of  work  done. 

266.  The  water  ferns.  The  water 
ferns  are  not  really  members  of 
the  true  fern  class  but  are  closely 
related  thereto.  Their  water  hab- 
itat is  striking.  Marsilia  (Fig. 
242)  has  peculiar  leaves,  looking 
like  the  four-leafed  clover,  and 
these  float  upon  water  or  stand 
slightly  above  it.  The  plant  is  fairly  abundant  in  greenhouses 
and  park  pools.  Salvinia  (Fig.  243)  and  Azolla  are  also  widely 
distributed  free-floating  water  ferns. 


FIG.  243.  A  water  fern  (Salvinia) 

The  plant  has  two  rows  of  hairy 
leaves  and  one  row  of  water  leaves 
(which  look  like  roots).  Natural  size 


HORSETAILS  OR  SCOURING  RUSHES  (EQUISETINE^E) 

267.  General  characteristics.  This  class  now  consists  of  one 
genus  (Equisetum)  and  a  few  species  (variously  estimated  at 
from  twenty  to  thirty).  The  class  and  closely  related  classes 
were  once  abundantly  represented,  and  as  tree-like  forms  were 
a  prominent  part  of  the  earth's  flora.  Fossil  remains  of  equise- 
tums  and  their  relatives  tell  interesting  stories  of  these  tree- 
like forms  which  lived  during  the  chief  coal-forming  periods. 
In  studying  present-day  forms  we  are  observing  the  remnants 
of  the  former  abundant  plant  life  of  this  class. 

Equisetums  now  live  chiefly  in  regions  unfavorable  to  most 
plants,  —  around  open  marshes,  in  sandy  wastes,  and  along 
railway  embankments.  They  have  hard,  rough,  siliceous,  and 


292 


PRACTICAL  BOTANY 


usually  unbranched 
about  the  joints  of 


FIG.  244.  Equisetum  arvense 

A,  a  plant  in  early  spring  condition  ;  r.s,  rhizome  ; 
s.b,  spore-bearing  branch,  with  the  collection  of 
sporophylls  (strobilus  or  cone)  at  its  tip;  f.b, 
b 


., 

ranch,  which  later  expands  as  in  B\ 
C,  one  sporophyll  from  the  cone,  showing  the  stalk 


foliage 


,  , 

(st)  and  several  sporangia  (sp).  D  and  E,  spore  with 
elaters.  A  and  B  one  half  natural  size,  C  magnified 
about  twenty  times,  and  D  and  E  greatly  enlarged 


stems.  The  small  leaves  form  a  sheath 
the  stem  (Fig.  244,  A,  B).  Most  of  the 
chlorophyll  is  borne  in  the 
stem,  and  little  or  no  chloro- 
phyll work  is  done  by  the 
leaves.  The  commonest  form 
now  living  is  known  as  the 
Equisetum  arvense. 

268.  Equisetum  arvense:  di- 
vision of  labor.    The  under- 
ground rootstock  is,  in  early 
spring,   stored   with  starchy 
food  that  was  made  by  the 
plant  during  the   preceding 
growing  season.    Very  early 
in  the  spring,  sometimes  be- 
fore the  last  snows  are  gone, 
there  grows  up  from  the  root- 
stock  one  sporophyll  branch 
(Fig.  244,  A).    This  has  no 
chlorophyll,    and  at  the  tip 
bears   the    sporophylls    in   a 
single  dense  spike  known  as 
a  cone  or  strobilus.  Soon  there 
appears  from  the  rootstock 
another  branch  which 
bears  chlorophyll.  The 
sporophyll  branch  soon 
dies,   but   the    chloro- 
phyll branch  subdivides 
extensively,  producing 
a  heavy,  bushy  plant, 
-the  "horsetail"  (Fig. 
244,  B).    This  grows 
throughout  the  season 
and  manufactures  food, 


THE  PTEKIDOPHYTES  293 

some  of  which  is  deposited  in  the  rhizome  and  used  in  pro- 
ducing next  season's  sporophyll  branch.  In  all  the  other  known 
species  of  Equisetum  the  sporophylls  grow  upon  the  same  branch 
that  does  the  chlorophyll  work. 

269.  Equisetum  arvense:  reproduction.  At  the  tip  of  the  spo- 
rophyll branch  is  the  collection  of  sporophylls.    Each  (Fig. 
244,  (7)  has  an  outer  shield-like  surface  which  grows  at  the 
end  of  the  sporophyll  stalk.    From  the  under  surface  of  the 
sporophyll  the  sporangia  grow.     The   spores  are  peculiarly 
wound  about  by  elaters  (Fig.  244,  D  and  E),  which,  as  they 
unroll  and  twist  about,  may  assist  in  spore  distribution. 

These  asexual  spores  germinate  almost  immediately  when 
ripe,  and  develop  into  gametophytes,  each  one  of  which  pro- 
duces but  a  single  kind  of  sex  organ ;  that  is,  a  gametophyte 
is  male  (produces  antheridia)  or  female  (produces  archegonia). 
After  fertilization  the  oospore  germinates  and  produces  a  new 
sporophyte,  thus  completing  the  life  cycle. 

THE  CLUB  MOSSES  (LYCOPODINE^E) 

270.  This  class  includes  the  two  genera  Lycopodium  and 
Selaginella,  though  fossils  show  a  former  abundance  of  related 
genera.    Both  are  very  widely  distributed  and  have  many 
species.    At  Christmas  time  these  plants  are  often  used  for 
decoration  and  are  called  "club  moss"  or  "ground  pine."   The 
rootstock  of  Lycopodium  often  grows  upon  or  just  beneath  the 
old  leaves,  frequently  sending  upright  branches  (Fig.  245) 
into  the  air. 

Selaginella  often  has  an  almost  upright  stem.  Roots  may 
arise  from  portions  of  this  stem  that  are  in  the  air.  Leaves 
are  spirally  arranged.  In  some  of  the  more  prostrate  Selagi- 
nella forms  the  leaves  have  become  differentiated  so  as  to 
appear  in  two  small  and  two  large  rows. 

271.  Reproduction  in  Lycopodium  and  Selaginella.  At  the  tips 
of  branches  strobili,  or  cones,  are  formed  in  most  species 
by  ordinary  foliage  leaves  becoming  sporophylls  without  losing 


294 


PRACTICAL  BOTANY 


their  chlorophyll.    These  sporophylls  are  closely  appressed 
(Fig.  245),  thus  forming  a  dense  cone.    In  a  few  species  the 

sporophylls  are  loosely 
arranged.  In  the  axils 
of  leaves  sporangia  are 
formed,  and  in  these  are 
large  numbers  of  asex- 
ual spores.  So  numer- 
ous and  so  light  are 
these  spores  that  they 
have  been  used  as  the 
commercial  article  now 
known  as  Lycopodium 
powder.  When  these 
spores  germinate  they 
produce  underground 
tuberous  gametophytes, 
upon  one  of  which  both 
sex  organs  may  form. 
Fertilization,  which  is 
extremely  difficult  to 
study  in  this  genus, 
occurs  underground. 
The  oospore  produces 
the  young  sporophyte, 
which  grows  up  from 
the  ground  somewhat 
as  does  the  seedling  of 
higher  plants. 

The  reproduction  of 
Selaginella  differs  from 
that  of  Lycopodium  in 
the  important  fact  that 
the  asexual  spores  are 


FIG.  245.  A  club  moss,  or  ground  pine 
(Lycopodium) 


The  horizontal  rootstock  with  its  roots  grows 
within  or  upon  the  humus.  The  upright  branches 
(A)  bear  green  leaves  and  strobili  (str),  also 
called  spikes  or  cones,  in  which  spores  are  formed. 
At  (7  is  shown  one  leaf  from  the  strobilus,  and 
upon  this  leaf  is  a  sporangium.  From  the  par- 
tially opened  sporangium  spores  escape.  At  B 
enlarged  spores  are  shown 


of  two  kinds,  one  very 
small  and  one  very  large. 


THE  PTEEIDOPHYTES  295 

This  results  in  the  production,  from  the  small  spore,  of  a  small 
gametophyte,  which  produces  sperms;  and  from  the  large 
spore,  of  a  large  gametophyte,  which  produces  the  egg,  and 
upon  which  thereafter  the  young  embryo  Selaginella  plant 
is  developed.1  All  the  groups  of  plants  higher  than  pterido- 
phytes  have  two  kinds  of  asexual  spores. 

272.  Pteridophytes  of  past  ages.  The  surface  of  the  earth 
has  undergone  many  changes  since  plants  began  to  live  upon 
it.  In  some  periods  of  the  earth's  history  conditions  favored 
certain  kinds  of  plants  and  these  flourished.  When  less  favor- 
able periods  came  these  successful  plants  were  greatly  reduced 
in  number  or  completely  exterminated.  We  have  records  of 
what  some  of  these  former  plants  were.  These  records  were 
made  by  the  plants  themselves,  for  when  they  died  they  some- 
times became  fossilized,  or  made  prints  in  soft  mud  or  other 
substances  which  afterward  hardened.  By  means  of  fossils 
much  is  being  learned  about  the  kinds  of  plants  that  used  to 
-exist.  In  many  cases  great  detail  of  structure  has  been  pre- 
served, and  many  important  facts  are  thus  established  with 
reference  to  the  history  of  our  existing  plants.  The  study  of 

1  In  some  cases  it  may  be  wise  to  go  more  into  the  details  of  the  repro- 
duction of  Selaginella,  and  for  such  use  the  following  facts  are  added  :  The 
terminal  cones  or  strobili  of  Selaginella  resemble  those  shown  in  Lycopodium. 
In  Selaginella,  however,  two  kinds  of  sporangia  with  two  kinds  of  spores  are 
formed.  One  sporangium  contains  large  numbers  of  small  spores,  while  the 
other  sporangium  contains  four  large  spores.  Both  kinds  are  asexual,  since 
both  are  formed  upon  the  sporophyte  by  cell  division.  The  small  spore  is 
called  the  microstore,  meaning  "little  spore"  ;  the  large  one  is  called  the  mega- 
spore,  meaning  "big  spore."  Similarly,  the  names  of  other  structures  relate 
to  the  size  of  the  spores  ;  as,  the  megasporangium  which  produces  the  mega- 
spore  is  borne  upon  the  megasporophyll,  and  the  microsporangium  which 
bears  the  microspores  is  borne  upon  the  microsporophyll.  We  have  in  Sela- 
ginella different  kinds  of  spores,  or  heterospory,  as  compared  with  similar 
asexual  spores,  or  homospory,  as  seen  in  the  other  ferns  that  we  have  studied. 
Each  spore  produces  a  particular  kind  of  gametophyte,  one  of  which  bears 
the  egg  and  the  other  the  sperm.  The  egg  is  fertilized  while  within  the 
female  gametophyte,  and  the  new  plant  begins  to  grow  from  the  same  posi- 
tion. If  the  structures  around  the  embryo  should  become  dry  and  hard,  and 
if  the  whole  should  undergo  a  resting  period,  we  should  have  the  structure 
that  we  call  the  seed  in  the  next  great  group  of  plants. 


296  PRACTICAL  BOTAKY 

fossil  plants,  or  paleolotany  as  it  is  called,  offers  a  field  of  great 
interest  to  the  specialist. 

Ferns  and  their  relatives  are  among  the  principal  fossil 
plants  concerning  which  paleobotany  has  given  us  informa- 
tion. The  introduction  of  vascular  tissue  furnished  structures 
better  fitted  for  preservation  than  there  were  in  the  less  rigid 
bryophytes  and  thallophytes.  It  has  been  definitely  deter- 
mined that  pteridophytes  and  other  plants  resembling  them 
were  once  more  abundant  and  larger  than  those  now  living. 
These  ancient  ferns  were  widely  distributed  over  the  earth. 
Certain  periods  (as  the  so-called  Carboniferous  Period)  were 
peculiarly  favorable  in  temperature  and  abundant  moisture  to 
the  growth  of  pteridophyte  types  of  plants,  and  they  grew  in 
size  and  profusion  much  greater  than  even  our  present  tree  fern 
forests  of  the  moist  tropics.  Their  range  extended  much  farther 
than  at  present.  Many  of  these  giant  forms  were  very  unlike 
our  existing  ferns,  horsetails,  and  club  mosses,  but  they  are 
the  ancestors  from  which  our  present  forms  have  descended. 

During  these  periods  there  also  lived  plants  which  are 
closely  related  to  some  of  the  seed  plants. 

273.  Coal  formation.  There  have  been  several  coal-forming 
periods  during  the  history  of  the  earth.  The  Carboniferous 
age,  however,  is  the  period  of  chief  coal  formation.  During 
this  time  almost  unimaginably  large  quantities  of  plant  life 
matured  and  fell  in  the  immense  swampy  areas  in  which  they 
grew.  As  is  true  when  Sphagnum  and  other  plants  in  peat 
bogs  decay  but  partially,  and  under  moderate  pressure  become 
peat,  it  is  thought  that  in  the  same  way  these  much  larger 
masses  of  plant  life  formed  immense  beds  of  partially  decayed 
plant  material.  After  a  long  period  of  such  growth  and  dep- 
osition of  plants  conditions  changed,  and  these  masses  of 
plant  material  became  submerged  and  then  buried  beneath 
layers  of  rock  and  earth.  The  surplus  water  in  the  beds  of 
plants  was  driven  away,  the  carbonaceous  material  was  pressed 
into  solid  masses,  the  oily  materials  were  pressed  out,  or,  as 
has  been  said,  under  the  pressure  the  coal  "  wept  bitter  tears 


THE  PTERIDOPHYTES  297 

of  petroleum." 1  Hard  coal  is  carbon,  with  some  ash-forming 
substances,  while  soft  coal  contains  ash-forming  substances  and 
volatile  matter  which  produces  smoke  when  the  coal  is  burned. 

The  amount  of  plant  material  required  to  form  an  ordinary 
bed  of  soft  coal  10  feet  in  thickness  is  estimated  to  be  about 
1500  feet  in  thickness.  There  may  be  several  layers  of  coal 
separated  by  layers  of  rock.  When  we  recall  that  the  United 
States  has  several  hundred  thousand  square  miles  of  coal 
lands,  we  obtain  some  notion  of  the  enormous  amount  of 
plant  growth  necessary  to  form  this  deposit.  It  has  been  esti- 
mated that  the  body  of  a  tree,  which  when  dry  weighs  11,000 
pounds,  contains  5500  pounds  of  carbon.  A  piece  of  ordinary 
soft  coal  10  feet  high  and  1  foot  square  might  weigh  as  much 
as  475  pounds.  The  pteridophyte  plant  body  is  not  nearly 
so  solid  as  our  woody  trees,  thus  necessitating  greater  bulk 
to  secure  a  corresponding  amount  of  carbon. 

274.  Summary  of  pteridophytes.  The  true  ferns  are  widely 
distributed  and  successful  plants.  The  possession  of  fibro- 
vascular  tissue  enables  these  plants  to  assume  a  position  of 
prominence  and  to  expose  chlorophyll  to  the  light  in  greater 
abundance  than  is  done  by  bryophytes.  Well-organized  woody 
stems  and  elaborate  leaf  structures  are  further  suggestions  of 
increased  ability  to  do  the  work  of  plants. 

Both  generations  of  the  true  ferns  bear  chlorophyll.  The 
gametophyte  is  simpler  than  that  of  bryophytes,  but  has  all 
the  structures  requisite  to  enable  it  to  live  for  a  time  in  an 
independent  way.  The  embryo  sporophyte  originates  from 
the  oospore  within  the  gametophyte  tissue.  The  sporophyte 
is  the  prominent  (often  perennial)  generation  of  the  plant. 
It  is  very  much  more  highly  differentiated  than  the  same 
generation  in  the  bryophytes.  Its  complex  sporangia,  formed 
upon  specialized  areas  of  the  leaf,  produce  and  distribute 
spores  in  very  large  numbers.  In  some  species  special  spo- 
rangium-bearing leaves  (sporophylls)  are  produced. 

1  Jordan,  David  Starr,  Science  Sketches,  essay  upon  "The  Story  of  a 
Stone.' 


298  PRACTICAL  BOTANY 

Pteridophytes  once  were  much  more  abundant  than  they 
now  are,  and  were  prominent  in  the  earth's  flora  during  the 
chief  coal-forming  ages.  Some  classes  have  ceased  to  exist 
and  others  are  now  represented  by  relatively  few  species. 

Once  the  horsetails,  or  scouring  rushes,  and  the  club  mosses, 
or  ground  pines,  contained  many  tree-like  forms.  Now  the 
first  class  contains  but  one  genus  and  a  score  or  more  of 
species,  and  the  second  contains  two  genera  and  several 
hundreds  of  species.  The  water  ferns  consist  of  four  highly 
specialized  genera.  In  the  Equisetinese  and  the  Lycopodinese 
sporophylls  are  arranged  in  a  spike  or  cone  (strobilus).  In 
one  genus  (Selaginella)  of  the  class  Lycopodinese  two  kinds 
of  asexual  spores  are  borne,  —  one  which,  upon  germination, 
produces  the  male  gametophyte,  and  one  which  produces  the 
female  gametophyte.  Within  this  female  gametophyte  the 
embryo  sporophyte  is  produced. 

275.  Classification: 

Pteridophytes 

Class  I.  Filicinese  (the  true  ferns).  Leading  genera  used  as  illustra- 
tions,— Pteris  (the  bracken  fern),  Alsophila  (a  tree  fern),  Adiantum 
(maidenhair  fern),  Camptosorus  (the  walking  fern),  Osmunda 
(royal  fern  and  Clayton's  fern),  Botrychium  (the  grape  fern), 
Onoclea  (sensitive  fern  and  ostrich  fern),  Salvinia  and  Marsilia 
(water  ferns) 

Class  II.  Equisetineae  (scouring  rushes,  or  horsetails).  Genus  used 
as  illustration,  —  Equisetum  (the  only  living  genus  of  the  class) 

Class  III.  Lycopodinese  (club  mosses,  or  ground  pines).  Leading 
genera  used  as  illustrations,  —  Lycopodium  and  Selaginella  (the 
living  genera  of  the  class) 


CHAPTER  XVIII 
GYMNOSPERMS 

276.  Introduction  to  spermatophytes.    The  highest  division 
of  the  plant  kingdom  is  the  seed  plants,  or  spermatophytes. 
The  name  means  "seed  plants."    This  is  the  division  usually 
thought  of  when  people  speak  of  plants,  since  in  it  are  the 
forms  that  make  up  the  conspicuous  flora  of  the  earth,  as  well 
as  those  that  furnish  most  of  our  food,  timbers,  fibers,  etc. 
It  is  the  division  with  which  agriculture,  horticulture,  garden- 
ing, and  many  of  the  industries  are  chiefly  concerned.    It  is 
highly  important  botanically  as  well  as  economically. 

There  are  two  great  classes  of  the  division,  —  the  gymno- 
sperms,  or  naked-seeded  spermatophytes,  and  the  angiosperms, 
or  inclosed-seeded  spermatophytes.  In  this  chapter  we  shall 
discuss  the  gymnosperms. 

277.  The  pine.    There  are  over  four  hundred  living  species 
of  gymnosperms.    Of  these  the  most  widely  distributed  mem- 
ber is  the  pine  (Pmws,  Fig.  246).    There  are  many  species  of 
pines,  and  while  but  a  few  kinds  are  usually  found  in  one 
locality,  the  resemblances  between  all  of  them  are  such  that 
one  is  likely  to  recognize  a  pine  if  once  he  has  carefully  noted 
the  characteristics  of  any  species. 

Sometimes  pines  form  dense  forests  of  tall,  straight  trees. 
They  often  stand  close  together.  It  is  only  when  they  grow 
thus  crowded  that  they  become  tall,  since  when  growing  alone 
in  open  regions  they  secure  ample  light  without  attaining  such 
a  height.  In  German,  American,  and  other  forest  plantations 
young  pines  are  planted  close  together;  then  when  they  have 
reached  toward  the  light  and  have  acquired  a  medium  height, 
some  are  removed  and  used,  and  their  removal  gives  the  remain- 
ing trees  more  space  in  which  to  spread.  Finally,  new  young 

299 


300 


PRACTICAL  BOTANY 


trees  are  planted,  and  they  attain  considerable  height  by  the  time 

the  last  of  the  oldest  crop  are  harvested  (see  Chapter  XXII). 

278.  The  vegetative  plant.    The  plant  has  a  heavy  central 

taproot  (Fig.  247),  which  extends  deep  into  the  soil.    From 

the  taproot  there  de- 
velops an  extensive 
system  of  roots,  some 
reaching  downward, 
and  even  more  out- 
ward, into  the  soil, 
in  this  way  forming 
an  abundant  root  sys- 
tem that  anchors  the 
plant  and  distributes 
the  youngest  rootlets 
in  favorable  positions 
in  the  soil. 

The  stem  is  gener- 
ally straight  and  the 
branches  usually  rise 
in  whorls.  Sometimes 
in  older  trees  many 
branches  have  died, 
and  but  one  or  two 
of  each  whorl  are  left. 
The  lower  branches 
are  usually  longest, 
the  top  ones  shortest, 
and  the  intermediate 
ones  grading  between 
these  extremes,  so  that  the  whole  tree  top  is  often  quite  cone- 
like  in  outline.  The  stem  and  branches  are  covered  by  a  heavy 
bark,  and  the  roots  by  a  bark  which  is  usually  not  so  thick. 
The  leaves  are  on  the  younger  branches.  The  needle  leaves  are 
most  conspicuous,  and  at  their  bases  and  on  the  terminal  buds 
are  the  brownish  scale  leaves. 


FIG.  246.  A  white  pine  (Pinus  Strobus) 

The  stem  is  almost  straight,  the  branches  stand 

approximately  at  right  angles  to  the  stem,  and  the 

top  is  irregularly  conical 


GYMNOSPERMS 


301 


The  needle  leaves  (Fig.  248)  are  borne  in  pairs,  in  threes, 
in  fives,  etc.,  the  number  varying  with  the  different  species. 
The  number  of  leaves  in  a  cluster  is  one  of  the  distinguishing 
characteristics  of  species ;  for  example,  the  white  pine  (Pinus 
Strobus)  has  five  leaves  in  a  cluster,  the  scrub  pine  (Pinus 
divaricata)  and  others  have  two  leaves  in  a  cluster,  the 


FIG.  247.  An  old  pine  tree  (Pinus  Strobus),  from  whose  roots  the  sand  has 
been  blown  away,  thus  exposing  the  taproot  and  killing  the  tree 

The  lateral  roots  have  been  removed  from  one  side,  but  they  show. at  the  right  of 

the  picture 

Georgia  long-leaf  pine  (Pinus  palustris)  has  three,  and  others 
may  have  a  variable  number  (2-5)  in  each  cluster. 

If  one  of  the  clusters  is  pulled  from  the  branch  and 
stripped  of  its  basal  scale  leaves,  there  will  be  seen  a  very 
small  whitish  branch  upon  which  the  needle  leaves  grow.  The 
needle  leaves  are  really  continuations  of  these  small  branches. 
The  inward  faces  of  the  leaves  are  so  arranged  that  all  of  one 
cluster  when  put  together  compose  a  cylindrical  leaf  mass. 


302 


PRACTICAL  BOTANY 


That  is,  when  two  leaves  compose  the  cluster,  the  leaf  branch 
is  divided  into  halves ;  when  three  or  five  are  in  one  cluster, 
the  branch  is  divided  into  three  or  five  parts. 

Leaves  of  pines  are  not  literally  evergreen,  as  is  sometimes 
supposed.  In  different  pines  the  leaves  remain  on  the  branches 
different  lengths  of  time.  In  all  species,  after  a  period  ranging 

from  two  to  four  years  the 
older  leaves  fall.  There 
is  no  definite  brief  period 
when  all  the  leaves  are 
discarded,  as  in  deciduous 
plants,  but  they  fall  a  few 
at  a  time. 

The  leaf  bases  are  spi- 
rally arranged  upon  the 
branches.  This  may  be  ob- 
served either  on  the  leafy 
branch  or  by  means  of  the 
leaf  scars  left  upon  branches 
from  which  the  leaves  have 
fallen. 

279.  The  structure  of 
needle  leaves.  The  hard  sur- 
face of  the  leaves  is  due 
to  the  very  heavy-walled 
epidermis  and  several  un- 
derlying layers  of  heavy- 
walled  strengthening  cells 
(sclerenchyma)  (Fig.  249).  Stomata  in  the  epidermis  are 
deeply  placed,  and  oftentimes  their  pores  are  clogged  with 
dust  so  that  they  appear  quite  dark.  Beneath  the  strength- 
ening tissue  is  the  chlorophyll  tissue,  through  which  run  the 
resin  ducts.  In  the  interior  of  the  leaf  is  the  pith  region, 
through  which  run  two  groups  of  fibrovascular  bundle  cells. 
The  well-protected  chlorophyll  tissue  seems  able  to  with- 
stand severe  conditions.  Its  temperature  changes  probably 


FIG.  248.  A  branch  of  a  pine 

At  the  left  (c)  is  a  one-year-old  cone,  and  at 
the  tip  of  the  shoot  (s)  a  very  young  cone 
(yc)  just  open  and  ready  to  receive  pollen. 
On  the  young  shoot  are  the  young  needle 
leaves,  and  at  the  tip  is  the  bud  (6),  which 
continues  the  growth  of  the  stem 


GYMNOSPERMS 


303 


occur  very  slowly.  It  conserves  its  water  supply  in  such  a  way 
that  it  lives  through  conditions  that  would  kill  deciduous 
leaves.  The  leaf  surface  is  greatly  reduced.  The  leaf  seems  to 


,ep 


rd. 


FIG.  249.  Part  of  a  cross  section  of  a  pine  needle  leaf 

ep,  the  epidermis,  upon  which  is  a  layer  of  cuticle ;  scl,  a  layer  of  heavy- walled  cells, 
or  sclerenchyma ;  st,  stomata  with  deeply  placed  guard  cells;  chl,  chlorophyll- 
bearing  tissue ;  rd,  resin  ducts  or  channels ;  bsh,  bundle  sheath  which  incloses 
-  two  vascular  bundles,  one  shown  at  vb 

have  secured  protective  form  and  covering  at  the  expense  of 
abundant  chlorophyll  exposure.  It  can  perhaps  begin  to  work 
earlier  in  the  season  and  work  later  than  can  deciduous  leaves. 


304 


PRACTICAL  BOTANY 


280.  The  branch  and  stem.  By  means  of  transverse  sec- 
tions of  branches  of  different  ages  the  general  structures  of 
the  stem  may  be  observed.  Innermost  is  a  small  pith  region, 
which  in  older  stems  is  compressed  until  it  is  not  usually 
noticeable.  Around  this  is  the  woody  tissue,  —  the  xylem  of 

the  fibrovascular  bundles. 
The  xylem  from  all  bundles 
is  joined  in  such  a  way  as  to 
form  a  solid  woody  (xylem) 
cylinder.  It  is  possible  to 
determine  the  age  of  the 
twig  by  counting  the  layers 
or  rings  of  wood.  If  two 
distinct  growth  periods  oc- 
cur, as  rarely  takes  place 
in  one  season,  two  rings 
of  wood  are  formed;  hence 
this  is  not  always  an  abso- 
lutely accurate  method  of 
determining  the  age  of  a 
stem. .  At  the  outer  edge  of 
the  woody  tissue  is  a  thin 
layer  of  cells,  the  cambium, 
which  separates  the  xylem 
and  phloem  cells.  The  cam- 
bium is  actively  growing 
tissue  which  produces  new 
xylem  within  and  new 
phloem  without.  The  tis- 


FIG.  250.  The  "grizzly  giant  big  tree" 
(Sequoia  Washingtoniana) 

The  20  X  100  foot  scale  will  help  to  show  the 
size  of  the  tree,  especially  if  one  pictures 
the  height  of  some  known  object  at  the  side 
of  this  scale.  This  tree  is  275  feet  high,  93 
feet  in  circumference  at  the  base,  and  64  feet 
3  inches  in  circumference  at  11  feet  from 
the  ground.  Original  negative  -by  Mode 
Wineman 


sues  outside  the  phloem, 
which  we  need  to  notice  in  this  connection,  are  the  green  bark 
and  dead  bark.  Dead  bark  is  constantly  being  formed  from 
green  bark  within,  as  green  bark  is  from  tissues  within  itself. 
This  results  in  making  the  dead  bark  constantly  thicker,  until 
finally  in  older  branches  and  stems  light  penetrates  through 
it  poorly  if  at  all,  and  chlorophyll  ceases  to  be  developed. 


GYMNOSPERMS 


305 


The  ridging  of  bark  is  due  to  the  fact  that  bark  on  young 
branches  and  stems,  when  the  stem  enlarges  and  produces 
new  tissue,  is  so  spread  that  longitudinal  crevices  are  formed. 
As  more  new  wood  and  bark  is  built  within,  the  spreading 
and  thickening  are  increased  and  ridges  and  crevices  become 
more  pronounced. 

281.  New  vegetative  growth.    The  production  of  branches 
and  needle  leaves  begins  in  the  late  summer  and  autumn. 
When  winter   arrives,    within  the 

large  buds  the  next  year's  growth 
is  complete  in  miniature.  The  next 
spring  the  bud  opens,  the  new 
branch  extends  (Fig.  248),  and  its 
needle  leaves  begin  to  elongate.  In 
a  very  short  time  the  elongation  is 
complete,  and  within  a  few  weeks 
the  young  needle  leaves  are  full- 
grown.  By  observing  the  number 
of  terminal  bud  scars  from  the  tip 
to  older  portions  of  a  branch  the  age 
of  a  branch  may  be  determined.  It 
will  be  interesting  to  ascertain  how 
many  years'  growth  can  be  deter- 
mined by  counting  the  bud  scars. 

282.  Significance  of  the  stem.    In  the  series  of  groups  of 
plants  that  we  have  hitherto  studied,  no  plant  stem  is  nearly 
so  complex  as  that  of  the  gymnosperm  trees.    In  the  ferns 
we  had  vascular  tissue,  but  in  pines  and  their  relatives  the 
vascular  tissue  is  organized  into  a  massive  woody  stem,  one 
often  of  immense  height  and  thickness  (Fig.  250).    In  the 
struggle  for  light  these  plants  have  been  highly  successful. 
Such  great  height  and  thickness  as  are  attained  involve  an 
equally  well-developed  root  system. 

To  industry  the  gymnosperm  stem  is  of  immense  signifi- 
cance. Pines  and  some  other  gymnosperms  and  many  angio- 
sperms  have  stems  upon  which  much  of  the  world's  work 


FIG.  251.    An  old  pine  cone 

which  has  opened  and  dropped 

its  seeds 

One  half  natural  size 


306 


PRACTICAL  BOTANY 


depends.  All  sorts  of  useful  and 
ornamental  manufactured  prod- 
ucts depend  upon  these  timbers, 
and  it  is  not  easy  to  overestimate 
their  value  to  mankind. 

283.  Asexual  reproduction.  Two 
kinds  of  cones  are  borne  upon  a 
pine  plant.    One  is  the  seed  cone 
(Fig.  251)  and  the  other  is  the 
staminate  cone.    An  examination 
of  a  young  seed  cone  will  at  once 
show   structures    somewhat   sim- 
ilar to  those  of  Lycopodium  and 
Selaginella.     The    cone 
is  composed  of  leaf -like 
structures,  on  the  up- 
per sides  of  which  ovules 
(megasporangia)    (Fig. 
252)  are  borne.    In  the 
ovules  large  cells,  the 
megaspores,  are  formed, 
but  one  in  each  mega- 
sporangium.  The  spore 
does    not   escape    from 
this     megasporangium. 
Before  relationships  be- 
tween    spermatophytes 
and  pteridophytes  were 
known,  the  megasporan- 
gium was  always  called 
an  ovule,  a  name  which 
is  still  largely  used. 

The  staminate  cones 
bear     the     microsporo- 

gametophy te,  which  bears  the  archegonium]i,  in      phylls  Or  stamens  (Fig. 
which  the  egg  is  formed ;  Pi,  pollen  tubes  from      5^r^  i  •  -u 

pollen  grains  which  lie  upon  the  tip  of  the  ovule       253),    Upon    Wmcn    are 


FIG.  252.  Diagram  of  part  of  a  seed  cone  of 
a  pine,  with  ovules  in  normal  position 

S,  sporophylls,  or  leaf-like  parts  of  the  cone ;  0, 
ovule  (megasporangium) ;  /,  the  covering  of  the 
ovule,  called  the  integument ;  FG,  the  female 


GYMNOSPERMS 


307 


borne  microsporangia.  In  the  microsporangia,  microspores  or 
pollen  are  formed.  They  have  peculiar  wing-like  outgrowths 
(Fig.  254),  which  help  to  buoy  them  upon  the  wind.  The 

pollen  is  shed  in  great  quantities 
and  may  be  carried  long  distances 
by  currents  of  air.  Indeed,  so 
extensive  are  the  showers  of 
microspores  of  pines  at  times, 
that  ignorant  people  have  im- 
agined that  they  were  showers 
of  sulphur  from  some  distant 
active  volcano.  Early  names  and 
more  recent  ones,  all  of  which 
are  still  used  for  the  structures 
of  the  staminate  cone,  are  sta- 
men for  microsporophyll,  pollen 
or  pollen  grains  for  microspores, 
pollen  sacs  for  microsporangia, 
and  staminate  flower  for  the 
strobilus  or  cone,  which  bears 
the  microsporophylls. 
284.  Pollination.  The  pollen  or  microspores  must  be  car- 
ried to  the  seed  cone  and  properly  placed  before  they  can 
develop.  The  proper  placing  of  pollen  is  called  pollination 
(Chapter  VIII).  In  pines,  young  seed 
cones  stand  upright  and  open  (Fig.  248) 
at  the  time  pollen  is  being  shed.  If  pollen 
grains  chance  to  come  into  the  seed  cones, 
they  slide  down  upon  the  leaf-like  parts 
to  the  base  where  the  sporangia  are  borne. 
There  by  means  of  a  sticky  secretion  they 
are  caused  to  adhere  to  the  tip  of  the  mega- 
sporangium,  and  pollination  is  completed.  Obviously,  if  wind- 
pollinated  plants  are  to  be  successful,  there  must  be  enor- 
mous quantities  of  very  light  pollen,  and  ovule-bearing  cones 
must  be  open  to  catch  pollen  that  chances  to  fall  upon  them. 


FIG.  253.  A  few  of  the  stamens 

and  pollen  sacs  from  a  staminate 

cone  of  the  pine 

Somewhat  enlarged 


FIG.  254.  An  enlarged 
pollen  grain  of  the  pine 

Much  magnified 


308 


PRACTICAL  BOTANY 


285.  The  gametophyte  and  fertilization.1  It  was  stated  in 
Sect.  283  that  the  megaspore  does  not  escape  from  the  mega- 
sporangium  or  ovule.  It  germinates  therein  and  produces 

the  gametophyte,  which 
sometimes  well-nigh  fills 
the  interior  of  the  ovule. 
The  old  megaspore  wall 
is  now  known  as  the 
embryo  sac.  At  the  end 
toward  the  open  tip  (the 
little  gate  or  micropyle) 
of  the  ovule,  this  game- 
tophyte develops  arche- 
gonia,  in  each  of  which 
an  egg  is  formed.  This 
is  therefore  a  female  ga- 
metophyte. 

Obviously  new  diffi- 
culties in  fertilization 
are  presented  in  the 
pine,  for  here  the  egg  is 
within  the  female  ga- 
metophyte, which  itself 
is  inclosed  by  layers  of 
ovule  tissue.  This  in- 
closing tissue  prevents 
the  sperm  from  swim- 
ming directly  to  the 
egg,  as  in  the  pterido- 
phytes.  After  the  microspore  or  pollen  grain  falls  upon  the 
megasporangium  its  contents  begin  to  produce  several  cells. 
From  the  wall  of  the  pollen  grain  there  grows  a  tube  into  which 

1  Under  ordinary  circumstances  it  is  not  wise  to  attempt  with  secondary- 
school  students  to  do  detailed  individual  laboratory  work  upon  the  game- 
tophytes  and  upon  fertilization  in  gymnosperms  and  angiosperms.  If  im- 
portant structures  can  be  shown  under  a  demonstration  microscope,  they 
will  prove  of  interest  and  value. 


FIG.  255.  The  tip  of  a  pollen  tube  of  a  pine 
at  the  time  it  has  almost  reached  the  egg 

Just  back  of  the  two  nourishing  cells  are  the 

two  darkly  colored  male  cells,  either  of  which 

may  fertilize  an  egg.   Much  magnified 


GYMNOSPERMS 


309 


pass  the  cells  formed  by  the  division  of  the  nucleus  of  the 
microspore.  This  tube  makes  its  way  through  the  tissue  of  the 
ovule,  toward  the  egg  (Fig.  252).  The  pollen  tube  really  begins 
to  grow  long  before  the  egg  is  formed.  Female  gametophyte 
and  pollen  tube  both  develop  slowly,  so  that  it  is  twelve  or 
thirteen  months  after  pollination  before  the  archegonium  is 
reached  by  the  tip  of  the  pollen  tube.  The  tip  of  the  pollen 
tube  opens  and  two  of  the  cells  that  were  carried  down  in  it 
pass  out  (Fig.  255).  Either  of  them  may  unite  with  the  egg 
to  produce  an  oospore.  The  other  one  disappears  after  a  time. 
These  are  the  male  cells.  We  should  call  them  sperms,  but 
they  do  not  have  cilia,  —  organs 
of  locomotion  which  are  parts  of 
sperms.  There  are  gymnosperms 
(Fig.  263)  which  have  real  sperms 
that  are  carried  to  the  archegonia 
by  pollen  tubes.  The  pollen  tube 
as  a  means  of  securing  fertilization 
is  of  great  importance,  and  this 
is  shown  in  even  a  more  striking 
way  in  angiosperms. 

286.  Embryo,  seed,  and  seedling. 
After  fertilization,  the  oospore 
develops  into  an  embryo  pine 
plant.  It  is  developed  within  the  old  female  gametophyte  from 
which  the  developing  embryo  derives  its  nourishment.  The 
wall  of  the  female  gametophyte  is  now  known  as  the  embryo 
sac  wall.  After  a  period  of  growth  the  embryo  has  developed 
root,  stem  tip,  and  leaves,  all  closely  packed  within  the  female 
gametophyte  tissue.  At  this  time  the  ovule  wall  becomes  dry 
and  hard  and  the  embryo  stops  growing.  The  whole  structure 
is  now  the  seed  (Fig.  256). 

When  the  pine  cone  opens,  two  years  or  more  after  the 
spring  when  pollination  occurred,  the  seeds  fall  from  it.  To 
each  seed  is  attached  a  wing,  which  sometimes  buoys  the 
seed  in  the  air,  thus  making  wide  distribution  more  probable. 


FIG.  256.   Diagram  of  the  seed 

of  a  pine  showing  the  embryo 

(new  pine  plant)  inclosed  within 

the  food  material 

At  the  right  tip  of  this  embryo  is 

the  root,  and  at  the  left  are  the 

seed  leaves  which  inclose  the  small 

stem  tip 


FIG.  257.  A  group  of  gymnosperm  cones,  of  which  all  except  B  are  carpellate 

A,    white   spruce    (Picea  excelsd),   one   half    natural   size;    B,   white   spruce; 

C,  western  hemlock   (Pseudotsuga  taxifolia),  one  fourth  natural  size,  branch 

and  staminate  cones  almost  natural  size;  D,  arbor  vitae  (Thuja  occidentalis), 

almost  natural  size 

310 


GYMNOSPERMS 


311 


The  seed  germinates  when  there  are  suitable  climatic  condi- 
tions. Its  embryo  swells,  bursts  the  seed  coat,  sends  the  root 
down  into  the  soil  and  the  stem  and  leaves  into  the  air,  and 
is  then  known  as  the  pine  seedling.  It  may  in  time  become  a 
new  pine  tree,  which  will  again  bear  cones  and  produce  seed. 
It  is  worthy  of  note  that  in  some  pines,  as  the  lodgepole  pine 
of  the  Rocky  Mountains,  the  cones  may  not  shed  their  seeds 
for  several  years,  sometimes  not  until  the  death  of  the  tree. 


FIG.  258.  Gymnosperm  cones  (continued) 

E,  "big  tree"  (Sequoia  Washingtonia) ,  two  thirds  natural  size;  F,  common 
juniper  (Juniperus  communis),  three  fourths  natural  size 

287.  The  Coniferales.  The  gymnosperms  are  subdivided  into 
four  living  groups :  the  Coniferales,  or  cone-bearing  gymno- 
sperms ;  the  Cycadales,  plants  which  in  general  form  resemble 
the  tree  ferns  and  some  of  the  palms ;  the  Grnetales,  a  group 
containing  but  three  genera,  which  in  form  are  so  unlike  one 
another  that  beginning  students  of  botany  would  not  think 
of  classifying  them  together;  the  CHnkgoale*,  represented  by 
one  tree  form.  By  far  the  largest  group  in  number  of  genera 
and  species  and  in  number  of  individuals  is  the  coniferales. 


312 


PEACTICAL  BOTANY 


The  coniferales  are  again  divided  into  two  families,  the 
Pine  family  and  the  Yew  family.  Practically  all  gymnosperms 
commonly  known  in  most  parts  of  the  United  States  belong  to 

the  Pine  family.  In  addi- 
tion to  the  widely  distrib- 
uted genus  Pinus  already 
discussed,  there  are  the 
spruces  (Picea),  which 
have  short,  stubby  needle 
leaves  (Fig.  257,  A  and^), 
close-set  branches,  and 
long,  generally  pendent 
cones.  The  spruces  are 
among  our  most  beauti- 
ful trees,  and  apprecia- 
tion of  them  is  shown 
by  the  extent  to  which 
they  are  being  planted 
for  ornamental  purposes. 
Their  detailed  structure 
and  reproductive  proc- 
esses resemble  those  of 
pines.  The  hemlock  trees 
(T&uga  and  Pseudotsuga) 
(Fig.  257,  C),  fir  trees 
(Abies),  and  the  southern 
bald  cypress  (Taxodiurti) 
are  members  of  this  fam- 
ily. Bald  cypress  is  one 
of  the  gymnosperms  that 
can  live  in  swampy  places. 
Its  roots  spread  enor- 
mously, near  the  surface. 
Often  from  these  roots  when  in  swampy  regions  there  grow 
upward  the  peculiar,  stump-like;  woody  structures  (Fig.  19) 
known  as  the  "  cypress  knees."  The  central  tissues  of  these 


FIG.  259.  A  large  cedar  tree  (Thuja  occi- 
dentalis) 

The  size  of  this  tree  is  indicated  by  a  com- 
parison with  the  man  standing  at  the  right. 
Photograph  by  the  Keyser  Photo  Company, 
Spokane,  Washington 


GYMNOSPEEMS 


313 


w  knees  "  are  quite  soft,  and  it  is  believed  that  they  furnish 
a  passageway  by  which  air  is  conveyed  to  the  roots.  The 
tamarack  (Larix)  is  common  in  bogs  in  the  north  temperate 
regions.  It  and  bald  cypress  are  deciduous  conifers.  The 
northern  white  cedar,  or  "  arbor  vitae  "  (Thuja)  (Figs.  257,  D, 
and  259),  and  southern  white  cedar  (Qhamcecyparis),  which 
often  are  low  shrubs  but  in  forests  become  large  trees,  are 
other  members  of  the  fam- 
ily. The  red  cedar,  juniper, 
and  low  juniper,  all  species 
of  the  genus  Juniperus  (Fig. 
258,  F),  are  some  of  this 
family's  most  widely  distrib- 
uted members.  Redwoods 
and  "big  trees"  (Sequoia) 
(Figs.  258,  J£;  250,  and 
260)  are  famous  over  the 
entire  world,  though  they 
now  grow  only  in  the  west- 
ern part  of  North  America. 
They  have  been  the  objects 
of  many  laudable  efforts  on 
the  part  of  people  who  de- 
sired to  preserve  them. 

The  American' yew,  called 
"  ground  hemlock,"  is  our 
only  representative  of  the 
Yew  family  (Taxacece).  It 
is  low  and  sprawling  in  growth.  Its  branch  resembles  in  form 
that  of  the  true  hemlock,  but  its  leaves  are  distinctly  pointed, 
while  those  of  the  hemlock  are  blunt.  Its  ripe  cone  consists 
of  a  central  hard  structure  which  contains  a  few  seeds,  and 
an  outer  coating  which  is  pulpy  and  brilliant  red  in  color. 

288.  Industrial  importance  of  conifers.  Several  species  of  nut 
pine  in  western  North  America  and  one  in  southern  Europe 
bear  edible  seeds,  which  are  of  considerable  value  as  food. 


FIG.  260.  "  Big  trees  "  of  California 

The  largest  living  trees  belong  to  this  group 

of  gymnosperms.  Original  negative  by  Mode 

Wineman 


FIG.  261.  The  southern  pitch  pine,  or  long-leaf  pine  (Pinus  palustris),  which 
is  used  as  a  source  of  turpentine  and  pitch 

Note  the  method  of  tapping  the  trees  to  secure  the  resinous  secretion.   Photograph 

hy  the  United  States  Division  of  Forestry 

314 


FIG.  262.  The  Douglas  fir 

A  gymnosperm  tree  of  immense  size  and  great  economic  importance  in  the  north- 
western United  States  and  Canada.  Photograph  by  the  Keyser  Photo  Company, 
Spokane,  Washington 


315 


316  PRACTICAL  BOTANY 

Pine  tar,  rosin,  and  oil  of  turpentine  (commonly  called  spirits 
of  turpentine)  are  valuable  products,  obtained  in  this  country 
principally  from  the  long-leaf  southern  pine  (Fig.  261). 

Timber  is  the  principal  product  of  our  conifers.  At  present 
more  than  three  fourths  of  the  timber  supply  of  the  United 
States  is  furnished  by  various  conifers,  especially  pines.  Dur- 
ing the  early  history  of  this  country  the  white  pine  (Pinus 
strobus)  was  almost  our  only  important  soft  wood.  Now  the 
long-leaf  pine  (Pinus  palmtris),  the  loblolly  pine  (Pinus  tcedd) 
of  the  southeastern  states,  and  the  bull  pine  (Pinus  ponder- 
osa)  of  the  Pacific  coast  and  the  Rocky  Mountain  region  are 
largely  utilized. 

Other  important  coniferous  timber  trees  are  two  eastern 
species  of  true  spruce  (Picea),  the  western  Douglas  fir  (Fig. 
262),  two  other  western  firs  (Abies'),  and  the  southern  bald 
cypress  (Taxodium).  Considerable  redwood  (Sequoia  semper- 
virens)  lumber  is  made,  though  preservation  of  redwood  for- 
ests is  limiting  their  output.  The  cypress,  larch,  and  most  of 
the  cedars,  because  of  their  durability,  afford  highly  valuable 
timber  for  all  kinds  of  out-of-door  work,  especially  for  posts 
and  railroad  ties.  Red  cedar  is  employed  in  making  moth- 
proof chests,  and  is  almost  the  only  wood  used  for  lead  pencils. 

Although  the  lightness  of  most  coniferous  woods  makes 
them  worth  less  for  fuel  (when  bought  by  the  cord)  than  the 
heavier  deciduous-leaved  species,  still  immense  quantities  of 
coniferous  woods  are  used  for  fuel. 

289.  The  Cycadales.  This  group  includes  nine  genera.  These 
are  found  in  tropical  and  semi-tropical  countries,  and  some  of 
them  are  found  only  within  comparatively  small  areas.  The 
stem  is  straight,  usually  unbranched,  and  bears  at  its  tip  a 
crown  of  leaves,  each  of  which  bears  many  hard  and  rigid  leaf- 
lets (Fig.  263).  In  some  species  the  stem  is  almost  or  entirely 
embedded  in  the  earth,  and  in  such  cases  it  is  like  a  long  tuber. 
The  stem  is  used  by  the  plant  as  a  storage  region  for  starch.  In 
some  countries  these  stems  are  collected  for  the  starch,  which 
after  extraction  is  sometimes  called  sago,  though  the  usual  sago 


GYMNOSPERMS 


317 


.of  commerce  is  made  from  a  true  palm.  This  practice  exposes 
some  cycads  to  danger  of  extinction,  but  others  which  are 
literally  weeds,  as  Zamia  integrifolia  and  Zamia  Floridana 
in  southern  Florida,  are  too  abundant  to  incur  this  danger. 


FIG.  263.  A  cycad  plant  showing  the  straight  stem,  the  crown  of  rigid  leaves, 
and  the  seed  cone 

There  is  a  common  greenhouse  cycad  (  Cycas  revoluta)  which 
is  often  improperly  called  sago  palm,  for  it  is  not  a  palm  at 
all.  This  plant  bears  large  staminate  cones,  but  the  carpels 
(megasporophylls)  are  borne  in  clusters  at  the  tip  of  the  stem. 
Most  of  the  cycads,  however,  bear  their  carpels  in  the  form  of 


318  PEACTICAL  BOTANY 

immense  cones  (Fig.  263),  the  largest  cone  known  in  the  plant 
kingdom  being  found  in  this  family. 

In  details  of  structure  of  the  vegetative  body  of  cycads, 
and  in  their  reproductive  structures  and  processes,  they  are 
of  great  interest  and  importance  to  special  students  of  botany. 
For  our  present  purposes,  however,  there  should  merely  be 
noted  (1)  the  fern-like  appearance  of  cycads;  (2)  the  stem 
and  leaves,  which  resemble  the  large  and  abundant  plants 
of  the  Carboniferous  age;  (8)  the  fact  that  in  some  cycads 
(Cycas  revoluta)  the  carpels  are  leaf -like,  with  sporangia  at 
the  margins  as  in  some  ferns ;  (4)  that  the  megaspore,  which 
is  scarcely  inclosed  within  the  ovule,  develops  a  female  game- 
tophyte,  which  bears  several  to  many  archegonia ;  (5)  that  the 
male  gametophyte  produces  usually  two  but  in  some  forms  it 
produces  several  true  sperms,  provided  abundantly  with  cilia 
and  able  to  swim  about  with  great  vigor  in  the  pollen  tube. 
These  facts  show  that  in  many  respects  cycads  are  more  like 
ferns  than  are  the  pines.  They  are  more  like  ancient  forms  of 
plants  than  like  present-day  ferns,  and  in  ancestry  are  very  old. 

There  were  formerly  many  species  of  plants  to  which  our 
present  cycads  are  related,  but  most  of  them  are  dead  and 
now  represented  only  by  their  fossils.  The  cycads  are  there- 
fore looked  upon  as  the  slowly  disappearing  remnants  of  a 
once  abundant  type  of  plant  life. 

290.  Other  groups.  The  G-netales  are  now  represented  by  but 
three  very  different  genera,  the  remnants  of  once  abundant 
and  successful  plants,  but  too  highly  specialized  for  use  in  this 
discussion. 

The  "maidenhair  tree"  (^G-inkgo)  —  a  tree  with  leaves 
(Fig.  264)  that  suggest  the  maidenhair  fern  —  is  becoming 
somewhat  generally  planted  as  a  shade  and  ornamental  tree. 
It  is  the  only  living  species  of  a  former  abundant  group 
(Grinkgoales)  of  gymnosperms. 

291.  Gymnosperms  of  past  ages.    It  has  been  stated  that 
pteridophytes  were  the  dominant  plants  in  the  Carboniferous 
age.    Fossils  of  ancestral  seed  plants  also  were  formed  during 


GYMNOSPERMS 


319 


the  same  age,  but  gymnosperms  did  not  become  really  abun- 
dant until  after  the  time  of  the  greatest  profusion  of  pterido- 
phytes.  In  this  next  age  gymnosperm  trees  became  dominant, 
and  large  numbers  of  fossil  remains  tell  strange  stories  to 
those  who  can  understand  them;  stories  of  many  kinds  of 
ancient  seed  plants,  of  giant  tree  trunks  when  gymnosperm 
trees  first  reached  high  into  the  air  as  a  result  of  the  struggle 
for  light,  and  of  seeds  when  the 
seed  habit  was  first  developing. 

In  those  times  gymnosperms 
were  almost  everywhere.  The 
"  big  trees "  and  redwoods 
extended  to  Greenland,  and 
cycads  and  other  groups  now 
well-nigh  extinct  grew  in  pro- 
fusion over  very  wide  areas. 
The  Pine  family  was  not  so 
abundant  then  as  were  other 
gymnosperms,  but  became  abun- 
dant later  and  to-day  is  a  fairly 
successful  group.  This  abun- 
dance of  pines  and  their  rela- 
tives in  some  regions  may  often 
be  explained  by  the  fact  that 
in  poor  soil  and  under  severe 
climatic  conditions  they  are 
exposed  to  little  competition 
with  other  trees. 

These  remnant  forms  of  the  formerly  luxuriant  gymnosperm 
groups  have  undergone  many  changes,  but  here  and  there  over 
the  earth  they  stand  as  still  living  evidences  of  the  class  of  plants 
that  dominated  before  the  highest  class,  the  angiosperms,  be- 
came the  leading  plants  of  the  earth.  Changes  in  the  climate  and 
in  the  physical  conditions  of  the  earth,  and  the  struggle  for  ex- 
istence, has  doubtless  often  reduced  or  eliminated  one  group 
of  plants  and  made  possible  the  dominance  of  another  group. 


FIG.  264.  A  branch  from  the 
"  maidenhair  tree  "  (Ginkgo) 

About  one  third  natural  size 


320  PEACTICAL  BOTANY 

292.  Classification: 

Spermatophytes 
Gym  no  sperm  s 

Class  I.  Coniferales.  Leading  genera  used  as  illustrations,  —  Pinus 
(pine),  Picea  (spruce),  Pseudotsuga  (Douglas  fir),  Tsuga  (hem- 
lock), Abies  (fir),  Taxodium  (bald  cypress),  Thuja  (cedar), 
Juniperus  (red  cedar,  juniper),  Sequoia  (redwoods  and  big  trees), 
Taxus  (yew) 

Class  II.  Cycadales.  Genera  used  as  illustrations, —  Cycas,  Micro- 
cycas  and  Zamia 

Class  III.    Gnetales.    Not  studied  in  any  detail 

Class  I V.  Ginkgoales.  Represented  by  Ginkgo  as  the  only  living 
genus 


CHAPTER  XIX 

ANGIOSPERMS 
COMPARISON  OF  THE  DIVISIONS  OF  PLANTS1 

293.  The  most  diverse  group  of  plants.  The  second  group  of 
spermatophytes,  the  angiosperms,  is  the  highest  group  of  the 
highest  division  of  the  plant  kingdom.  The  number  of  indi- 
viduals of  this  class  is  very  great.  Only  one  other  group,  the 
fungi,  compares  favorably  with  it  in  number  of  species  and 
of  individuals.  There  is  a  difference  of  opinion  as  to  how 
many  angiosperms  there  are,  but  all  agree  that  there  are  over 
100,000,  and  doubtless  there  are  many  undescribed  species 
yet  to  be  added.  Not  only  is  the  number  of  species  and  num- 
ber of  individuals  very  great,  but  the  variation  in  form  and 
habit  covers  almost  every  imaginable  condition.  There  are 
submerged  water  plants,  free-floating  plants,  plants  growing 
in  water  part  of  the  time  and  on  land  part  of  the  time.  They 
grow  in  some  regions  so  dry  and  so  exposed  that  it  would  seem 
nothing  could  live  ;  they  thrive  luxuriantly  in  the  tropics,  and 
they  even  live  upon  the  ice  in  frigid  regions.  They  may  be  epi- 
phytic, may  live  as  vines  upon  other  plants;  or  may  be  para- 
sites, saprophytes,  and  even  carnivorous  plants.  In  form  the 
angiosperms  range  from  diminutive  floating  disks  to  gigan- 
tic trees.  In  length  of  life  they  range  from  forms  that  pass 
from  adult  plant  to  plantlet  and  to  adult  again,  several  times 
each  season,  to  individual  plants  which  live  to  be  several  cen- 
turies old.  The  class  contains  plants  that  produce  our  most 
necessary  foods,  and  others  that  are  deadly  poisons. 

1  This  chapter  completes  the  study  of  the  great  groups  (Chapters  X-XIX) 
in  the  order  of  their  increasing  complexity.  Since  there  have  already  been 
several  chapters  dealing  with  seed  plants,  the  present  one,  while  adding  new 
material,  is  also  somewhat  in  the  nature  of  a  summary. 

321 


322  PRACTICAL  BOTANY 

294.  The  youngest  and  most  successful  group.   As  a  group 
these  are  the  youngest  plants.    Even  within  the  fossil  beds  in 
which  gymnosperms  are  abundantly  represented  there  appear 
few  structures  that  can  be  interpreted  as  belonging  to  the  an- 
giosperms.    Geologically  the  angiosperms  are  of  recent  origin. 
The  pteridophytes  and  gymnosperms  in  their  periods  of  great- 
est luxuriance  comprised  many  diverse  forms  and  many  indi- 
viduals.   In  the  present  age  it  seems  that  we  are  witnessing 
the  ascendancy  of  the  highest  and  most  successful  plants. 

295.  The   most  complex  group  of   plants.    In  Chapter  II 
there  were  outlined  the  leading  facts  regarding  the  way  in 
which  angiosperms  are  nourished  and  in  which  they  repro- 
duce themselves.    In  subsequent  chapters  many  details  were 
given  upon  these  two  aspects  of  the  work  of  plants.    It  has 
certainly  been  made  evident  that  the  structure  and  habits  of 
life   of  angiosperms  are  complex,  and  enable  them  to  live 
under  a  very  wide  range  of  conditions.    There  are  genera  and 
species  of  angiosperms  some  of  which  are  able  to  live  in  almost 
any  kind  of  environment  in  which  plant  life  is  possible. 

The  reproductive  structures  of  angiosperms  have  much  to 
do  with  the  success  of  the  class.  Many  other  features  of  the 
group  are  of  such  importance  as  to  demand  an  entire  chapter, 
and  these  are  fully  discussed  under  separate  chapter  headings 
(Chapters  II-IX,  and  XX-XXVI).  Certain  details  of  seed 
formation  and  the  relations  that  angiosperms  hold  to  other 
groups  are  presented  in  this  chapter. 

296.  The  angiosperm  flower.  Collections  of  sporophylls  such 
as  were  seen  in  the  pines  are  sometimes  called  flowers.  In  the 
angiosperms  there  are  usually  leaf-like  organs  about  the  spo- 
rophylls, and  the  presence  of  these  is  popularly  considered  as 
essential  to  the  flower.    These  leaves  or  bracts  are  not  neces- 
sarily colored,  and  indeed  often  are  not  so.     Furthermore, 
there  are  angiosperm  flowers  that  do  not  have  floral  leaves ; 
consequently  no  closely  drawn  line  can  be  placed  between  the 
strobilus,  or  cone  of  gymnosperms,  and  the  flower  of  angio- 
sperms.   The  essential  structures  of  a  flower  are  stamens  or 


ANGIOSPERMS  323 

microsporophylls,  and  carpels  or  megasporophylls.  The  carpel 
is  also  commonly  called  a  pistil.  A  carpel  is  one  megasporophyll 
and  a  pistil  may  be  one  or  several  carpels  joined  together  as 
was  shown  in  Chapters  II  and  VII. 

The  presence  and  nature  of  the  floral  structures  and  seeds 
in  this  group  and  in  the  gymnosperms  has,  at  various  times, 
given  rise  to  different  names  for  the  division.  Flowering  plants 
or  seed  plants  are  the  most  common  names,  and  are  good 
names.  Phanerogams,  meaning  "reproduction  easily  seen,"  was 
applied  when  less  was  known  of  the  intricacies  of  reproductive 
processes.  At  that  time  pteridophytes,  bryophytes,  and  thallo- 
phytes  were  classed  together  as  Cryptogams,  meaning  "  repro- 
duction difficult  to  see."  These  names  are  still  used  by  many 
people.  An  interchange  of  the  names  would  better  fit  the  facts. 

297.  The  stamen  and  microspores.  In  Chapter  II,  Sect.  21, 
it  was  stated  that  the  tip  of  the  stamen  is  the  anther.  It  is 
borne  by  a  slender  stalk  (the  filament).  In  a  transverse  sec- 
tion of  an  anther  (Fig.  99)  there  appear  the  spaces  in  which 
pollen  grains  (microspores)  are  formed.  In  a  young  anther 
four  spore-forming  regions  (sporangia)  may  be  seen,  but  by 
the  time  each  sporangium  has  matured  its  spores,  pairs  of 
sporangia  have  joined  by  the  breaking  down  of  the  separating 
walls.  In  a  mature  anther,  therefore,  but  two  pollen  sacs  are 
present.  Special  arrangements  exist  for  the  opening  or  dehis- 
cence  of  the  anther  (Fig.  100).  The  anthers  may  open  length- 
wise, by  means  of  terminal  pores,  or  in  other  ways. 

Since  they  are  formed  by  division  of  cells,  it  is  evident  that 
the  pollen  grains  are  asexual  spores.  When  mature,  each  one 
consists  of  a  heavy  outer  wall,  an  inner  wall,  cytoplasm,  and 
nucleus.  Often  there  are  starch  foods  stored  in  the  pollen  grains. 
Frequently  pollen  grains  begin  to  germinate  before  they  leave 
the  anther,  so  that  two  nuclei  may  be  seen  within  the  spore  wall. 

The  pollen  grains  must  be  placed  upon  the  tip  of  the  pis- 
til before  further  development  occurs.  This  process  consti- 
tutes pollination^  to  which  a  chapter  has  already  been  given 
(Chapter  VIII). 


324 


PRACTICAL  BOTANY 


298.  The  carpel,  megaspore,  and  female  gametophyte.1  The 

carpel  or  pistil  consists  of  three  parts :  the  enlarged  base  which 

is  the  ovary,  in  which 
one,  several,  or  many 
ovules  are  borne ;  the 
elongated  portion  above 
the  ovary,  the  style;  at 
the  tip  of  the  style,  the 
stigma,  which  in  different 
plants  is  divided  or  ex- 
panded in  various  ways 
(Figs.  110  and  111). 
When  ripe,  the  stigma 
secretes  a  sticky  fluid, 
or  produces  a  coating 
of  hairs  by  means  of 
which  pollen  grains  are 
caused  to  adhere  to  it. 
The  style,  which  may 
have  lifted  the  stigma 
into  an  exposed  position, 
now  serves  as  tissue 
through  which  pollen 
tubes  may  grow  to  the 
ovules.  The  ovary  con- 
tains a  special  cavity  in 
which  ovules  are  borne 
in  a  variety  of  positions 
(Fig.  102).  The  ovule 
may  be  upright  or  more 
or  less  recurved  toward 
its  base.  The  surface  of 


01 


FIG.  265.  Diagram  of  the  ovule  of  an  angi- 
ospermous  plant,  showing  the  parts  of  the 
ovule,  the  outer  integument  (oi),  the  inner 
integument  (i),  the  micropyle  which  is  the 
opening  between  the  parts  of  the  inner  in- 
tegument, and  the  pollen  tube  which  has 
grown  through  the  micropyle 

In  the  interior  of  the  ovule  is  the  embryo  sac, 
within  which  are  the  tip  of  the  pollen  tube,  the 
egg  and  a  sperm  in  process  of  uniting.  Near  the 
egg  are  the  two  synergid  cells,  in  the  center  of 
the  sac  are  the  two  embryo  sac  cells  and  the 
other  male  cell,  which  unite  to  form  the  endo- 
sperm cell,  and  at  the  end  of  the  sac  are  the  an- 
tipodal cells,  which  usually  disintegrate  after  a  . 
time.  After  fertilization  the  egg  proceeds  to 
form  the  embryo  of  the  new  plant 


the  ovule  consists  of  one 
or  two  integuments,  which  at  the  tip  do  not  quite  cover  the 
inner  tissue.   This  open  tip  is  the  mieropyle.  Similar  structures 
i  See  footnote  on  page  308. 


AKGIOSPEEMS 


325 


of  the  ovule  were  seen  in  the  gymnosperms.  Within  the  cen- 
tral tissue  of  the  ovule  a  megaspore  is  formed.  Upon  its  for- 
mation this  megaspore  at  once  proceeds  to  grow  to  produce 
the  female  gametophyte.  The  wall  enlarges  and  elongates  to 
form  the  embryo  sac,  and  the  nu- 
cleus divides.  One  new  cell  passes 
to  each  end  of  the  developing  sac 
and  soon  divides  again,  thus  pro- 
ducing two  cells  at  each  end,  or 
four  in  all.  Each  of  these  divides, 
thus  producing  eight  cells  in  all. 
One  passes  from  each  end  toward 
the  center  (Fig.  265),  and  these 
two  unite  to  produce  the  endosperm 
cell  from  which  the  endosperm  of 
the  seed  develops  later.  The  female 
gametophyte  at  this  time  consists 
of  seven  cells  inclosed  within  the 
old  megaspore  wall  or  embryo  sac. 
In  the  micropylar  end  of  the  game- 
tophyte are  three  cells,  the  central 
one  of  which  is  the  egg,  and  on 
each  side  of  the  egg  is  a  cell  which 
resembles  the  egg.  These  are  called 
the  synergids  or  helper  cells.  They 
may  nourish  the  egg,  or  possibly 
may  assist  in  directing  the  pollen 
tube  when  it  enters.  In  the  oppo- 
site end  of  the  embryo  sac  are  three 
antipodal  cells,  which  usually  dis- 
appear soon  after  they  are  formed, 
and  near  the  middle  of  the  embryo  sac  is  the  endosperm  cell. 
299.  Fertilization.  After  pollen  grains  or  microspores  have 
fallen  upon  the  stigma  the  outer  spore  wall  breaks,  and  from 
the  inner  wall  there  extrudes  the  beginning  of  the  pollen  tube. 
The  tube  tip  enters  the  stigmatic  tissue  and  forces  its  way 


FIG.  266.  Germinating  pollen 
grains 

The  pollen  grains  (g)  have  been 
deposited  upon  the  stigma.  The 
roughened  surface  of  the  stigma 
is  made  by  cell  extensions  or  pa- 
pillae (p).  Pollen  tubes  (f)  grow 
from  the  grains  through  the  tis- 
sue or  along  the  central  canal  (c) 
until  they  reach  the  ovule.  Only 
a  small  part  of  the  stigma  and 
style  are  shown  in  this  cut 


326  PRACTICAL  BOTANY 

through  the  central  softer  tissues  of  the  style.  It  does  not 
make  a  passageway  by  forcing  aside  the  tissue,  but  by  means 
of  its  own  secretions  (enzymes)  it  breaks  down  these  cells, 
and  they  doubtless  furnish  nourishment  to  the  growing  pollen 
tube  (Figs.  107  and  266).  The  tube  usually  makes  its  way 
down  the  center  of  the  style,  then  along  the  wall  of  the  ovary 
cavity,  and  finally  turns  across  to  the  micropyle  of  the  ovule. 
It  then  grows  through  the  tissues  to  the  end  of  the  embryo 
sac.  In  some  cases  (elm  and  walnut)  the  pollen  tube  grows 
down  to  the  base  of  the  ovule,  then  up  through  it,  and  finally 
reaches  the  egg. 

While  this  long  growth  of  the  pollen  tube  has  been  taking 
place,  development  within  it  has  also  occurred.  From  the  single- 
celled  microspore  there  now  have  developed  three  cells,  which 
are  contained  in  the  tip  of  the  tube.  Two  of  these  are  male 
cells  and  can  function  as  sperms,  though  they  are  non-ciliated. 
The  other  is  a  nutritive  cell,  which  goes  forward  within  the 
tip  of  the  pollen  tube  and  is  an  important  factor  in  its  growth. 

When  the  tube  reaches  the  embryo  sac  it  opens,  the  male 
cells  pass  out,  and  one  of  them  unites  with  the  egg  (Fig.  265). 
In  many  cases,  and  perhaps  generally,  the  other  male  cell 
passes  down  and  unites  with  the  endosperm  nucleus,  which 
was  formed  by  the  union  of  two  female  gametophyte  cells.  This 
results  in  a  cell  that  is  the  union  of  three  cells, — a  phenome- 
non not  known  elsewhere  in  the  plant  kingdom.  The  ordinary 
fertilization  of  the  egg  and  this  added  phenomenon  of  union 
of  a  male  cell  and  the  endosperm  cell  is  known  as  double  fer- 
tilization. Its  significance  is  not  understood,  but  it  is  notably 
true  that  angiosperms  present  the  first  case  in  seed  plants 
wherein  the  female  gametophyte  has  two  periods  of  develop- 
ment, one  before  fertilization  and  one  afterward,  and  it  may 
be  that  double  fertilization  is  related  to  this  second  period  of 
growth  of  the  female  gametophyte.  During  the  period  while 
the  oospore  is  growing  into  the  embryo  plant,  the  endosperm 
cell  is  growing  into  the  endosperm  that  is  often  found  in  ripe 
seeds  (Figs.  126  and  128). 


ANGIOSPERMS 


327 


300.  The  embryo  and  seed.  After  its  formation  the  oospore 
at  once  proceeds  to  divide  and  to  form  the  new  plant.  First 
it  divides  in  such  a  way  as  to  form  a  suspensor,  which  usually 
attaches  the  embryo  to  the  wall  of  the  embryo  sac  (Fig.  267). 
The  other  end  of  the  embryo  differentiates  a  root  tip,  a  stem 
tip,  and  one  or  two  (some- 
times several)  leaf  tips. 
Sometimes  there  is  but 
one  leaf  tip,  which  grows 
from  the  end  opposite  the 
root  tip,  while  the  stem 
is  laterally  placed.  This 
is  true  in  those  plants 
which  are  called  monocoty- 
ledons (meaning  "  one  seed 
leaf").  In  other  plants, 
the  dicotyledons  (meaning 
"  two  seed  leaves  "),  the 
two  (rarely  more)  seed 
leaves  arise  laterally  and 
the  stem  tip  is  terminal. 
After  these  structures 

FIG.  267.    Diagram   of   the   ovule,    em- 
bryo sac,  and  embryo  of  shepherd's-purse 
(Capsella) 


—  ouint 


The  parts  shown  are  the  outer  integument 
(ou  int) ,  inner  integument  (in  int) ,  embryo 
sac  wall  (esw),  suspensor  cells  (susp  c) ,  root 
region  (r  r),  stem  region  (st  r),  and  seed 
(si) 


have  been  formed  the  in- 
tegument walls  become 
dry  and  hard,  and  the  seed 
is  completed.  It  may  be 
shed  and  grow  at  once,  or 
it  may  lie  upon  the  ground 
until  the  next  year.  Some 
seeds  lose  then*  vitality  soon  after  they  are  formed.  In  other 
cases  (cocklebur  and  some  desert  plants)  they  may  lie  in  the 
ground  for  one  to  several  years  and  then  grow.  Some  seeds 
may  be  kept  for  several  years  (wheat,  corn,  etc.)  and  retain 
in  part  or  entirely  their  ability  to  germinate,  but  usually  they 
lose  their  vitality  after  a  few  years  at  the  most.  The  relations 
between  seed  and  fruit  are  difficult  to  define.  The  ripened 


328  PRACTICAL  BOTANY 

ovule  is  the  seed.  When  any  other  structure  is  added  the 
result  is  the  fruit.  For  example,  if  the  ovary  wall  hardens 
about  the  seed,  as  in  the  sunflower,  we  have  the  kind  of  fruit 
called  an  akene.  In  the  stony  fruits,  as  the  peach,  the  ovary 
wall  divides,  the  inner  part  produces  a  hard  covering  to  the 
seed,  and  the  outer  part  produces  a  pulpy  flesh.  In  an  apple 
the  calyx  is  joined  to  the  wall  of  the  ovary,  the  seeds  are 
inclosed  within  ovary  cavities,  the  ovary  wall  ripens  into  the 
core,  and  the  calyx  ripens  into  the  greater  part  of  the  apple 
fruit.  A  transverse  or  longitudinal  section  of  an  apple  or  pear 
will  usually  enable  one  to  determine  what  part  of  the  fruit  is 
the  ripened  calyx  and  what  part  is  the  ovary  wall.  In  general 
it  may  be  said  that  the  fruit  is  the  seed  plus  anything  else 
that  ripens  with  it.  In  plants  such  as  the  bean  (Fig.  15),  while 
seeds  are  maturing  the  entire  carpel  grows  and  the  ovary  ripens 
into  the  fruit  known  as  the  pod.  (See  Chapter  IX  for  discus- 
sion of  the  germination  of  seeds  and  the  development  of  the 
parts  of  the  adult  angiospermous  plant.) 

301.  The  life  cycle  of  angiosperms.  The  flowering  plants 
which  we  ordinarily  see  are  the  sporophytes,  since  they  pro- 
duce asexual  spores.-  Angiosperm  sporophytes  are  highly  or- 
ganized, with  complex  and  divergent  types  of  roots,  stems, 
and  leaves,  and  living  with  almost  every  possible  habit  in 
every  possible  region.  So  varied  in  form  and  habit  are  these 
plants  that  no  single  type  or  few  types  can  adequately  repre- 
sent them. 

The  flower  is  primarily  organized  to  produce  asexual  spores, 
but  later  is  also  used  for  sexual  reproduction.  In  fact  so  closely 
related  are  these  two  reproductive  stages  that  people  some- 
times erroneously  speak  of  the  stamen  as  the  male  structure  of 
the  flower  and  the  pistil  as  the  female  structure.  No  confu- 
sion need  arise  with  the  stamen,  since  it  is  the  microsporophyll 
which  produces  the  pollen  grains.  Later  the  pollen  grain  ger- 
minates and  produces  the  male  gametophyte.  The  pistil  offers 
more  difficulty,  for  although  it  first  produces  a  megaspore,  that 
cell  produces  the  female  gametophyte  within  the  ovule.  The 


ANGIOSPERMS  329 

pistil  is  primarily  an  asexual  reproductive  structure,  and  later 
is  given  the  appearance  of  sexuality  by  the  fact  that  the  game- 
tophytes  develop  within  it  instead  of  free  from  the  sporophyll, 
as  is  true  in  the  pteridophytes. 

There  is  great  reduction  in  both  gametophytes.  In  gymno- 
sperms  there  were  more  cells  in  the  male  gametophyte,  and 
in  some  gymnosperms  (  Cycads)  not  only  are  true  sperms  pres- 
ent, but  in  some  cycads  there  may  be  several  sperms.  In 
angiosperms  there  are  but  two  male  cells  and  one  nutritive 
cell  in  the  male  gametophyte.  The  female  gametophyte  of 
gymnosperms,  while  inclosed  in  the  ovule,  is  a  compact  tissue 
that  bears  several  to  many  archegonia.  In  angiosperms,  at  fer- 
tilization time,  the  female  gametophyte  consists  of  but  seven 
cells.  The  tissue  is  not  compact.  There  is  but  one  egg,  and 
it  is  borne  without  an  archegonium.  Accompanying  this  great 
reduction  of  the  female  gametophyte  are  the  added  phenomena 
of  double  fertilization  and  the  second  period  of  gametophyte 
growth  resulting  in  endosperm  formation. 

The  ovules  are  inclosed  within  the  sporophyll  that  bears 
them.  This  necessitates  a  much  more  extensive  growth  of 
pollen  tubes  in  order  that  fertilization  may  be  effected.  The 
pollen-tube  habit  is  so  well  developed  in  angiosperms  that  in 
some  plants,  whose  styles  are  several  Inches  in  length,  fertili- 
zation will  have  occurred  within  a  few  hours  after  pollination. 
This  is  of  especial  interest  when  we  recall  (1)  that  in  the 
pine  about  thirteen  months  elapse  after  pollination  before  the 
pollen  tube  grows  through  the  ovule  tip  to  the  egg ;  and 
(2)  that  in  angiosperms  the  pollen  grains  sometimes  alight 
at  a  distance  from  the  egg  that  is  hundreds  of  times  greater 
than  in  gymnosperms,  and  grow  fast  enough  to  make  their 
way  to  the  egg  within  a  few  hours. 

Gymnosperms  are  ancient  plants,  and  seed-forming  processes 
in  them  occur  slowly.  Angiosperms  are  recent  plants,  and  seed 
formation  in  them  occurs  often  very  rapidly  and  in  enormous 
quantity.  The  abundant  and  effective  production  of  seed  is 
an  important  factor  in  the  present  success  of  the  angiosperms. 


330  PRACTICAL  BOTANY 

COMPARISON  OF  THE  GREAT  DIVISIONS  OF 
THE  PLANT  KINGDOM1 

302.  Evolution  of  plants.   The  leading  classes  which  com- 
pose the  four  great  divisions  of  plants  have  been  discussed, 
and  type  forms  have  been  described  in  most  of  these  classes. 
It  has  doubtless  been  made  evident  throughout  Chapters  X- 
XIX  that  some  groups  of  plants  have  developed  from  others. 
This  process  is  known  as  the  evolution  of  plants.    The  oldest 
plants  of  the  earth  were  very  simple,  and  from  them  more 
complex  ones  have  gradually  developed.    The  simplest  plants 
that  are  now  living  probably  have  changed  greatly  from  the 
oldest  simple  plants.    It  is  even  probable  that  some  simple 
plants  that  are  now  living  have  developed  from  complex  forms. 

While  we  compare  one  living  group  with  another,  we  must 
keep  in  mind  that  a  higher  group  of  living  plants  has  not 
necessarily  developed  from  one  of  the  lower  living  groups, 
but  rather  that  often  in  past  ages  a  common  ancestry  gave  rise 
to  both.  The  lower  group  has  probably  changed  less  than  the 
higher  one.  While  higher  groups  have  evolved  from  lower 
ones,  it  is  also  possible  that  certain  lower  groups  of  dependent 
plants  have  evolved  from  higher  groups.  This  means  that 
evolution  may  lead  toward  greater  complexity,  as  usually  hap- 
pens, or  may  lead  toward  greater  simplicity  in  structure.  In 
this  summary  of  the  divisions  we  shall  have  in  mind  chiefly 
two  groups  of  characters,  —  those  which  relate  to  nutritive 
work  and  those  which  relate  to  reproductive  work. 

303.  Thallophytes.  The  thallophytes  live  almost  entirely  in 
water  or  in  moist  situations,  so  that  usually  a  fairly  constant 
water  supply  is  present.  They  are  not  differentiated  into  roots, 
stems,  and  leaves,  and  there  is  little  difference  between  the 
cells  that  compose  a  plant.    There  are  two  subdivisions:  the 

1  In  connection  with  this  general  summary  the  pupil  should  reread  each 
of  the  summaries  of  groups  and  classifications  as  they  are  found  at  the  close 
of  chapters,  and  review  briefly  the  laboratory  work  that  has  been  done. 
Unless  this  is  done  with  care  the  final  summary  will  prove  very  difficult. 


ANGIOSPERMS  331 

algae,  or  chlorophyll-bearing  thallophytes,  and  the  fungi,  or 
those  which  do  not  bear  chlorophyll.  One  group,  therefore,  is 
independent  in  nutrition,  the  other  dependent. 

The  fungi  are  thought  to  have  descended  from  the  algae. 
On  account  of  the  dependent  habit  and  the  loss  of  chlorophyll 
there  has  been  evolved  this  group  of  thallophytes  which  in 
structure  and  reproduction  (Mucor,  Saprolegnia)1  often  resem- 
ble algae.  Others  live  as  saprophytes  (many  bacteria,  Mucor, 
some  toadstools  and  mushrooms,  Penicillium,  yeasts)  ;  others 
as  parasites  (many  bacteria,  Saprolegnia,  grape  mildew,  lilac 
mildew,  corn  smut,  wheat  rust,  tree-destroying  toadstools)  ; 
others  as  mutualists  (the  lichens).  The  dependent  habit  of  liv- 
ing has  often  resulted  in  limiting  parasites  to  a  few  kinds  of 
host  plants  without  which  they  cannot  live.  It  is  thought  that 
members  of  the  simplest  group  of  thallophytes,  the  bacteria, 
have  descended  from  forms  like  the  blue-green  algae,  and  that  as 
they  were  enabled  to  live  more  and  more  completely  as  parasites 
and  saprophytes  their  nutritive  structures  became  more  and 
more  simple,  until  now  they  are  reduced  almost  to  the  lowest 
possible  limit.  It  is  generally  supposed  that  different  groups 
of  fungi  are  descended  from  different  groups  of  algae. 

An  important  series  in  increasing  complexity  of  nutritive 
and  reproductive  structures  is  shown  in  the  algae.  In  nutri- 
tive structures  we  have  first  single-celled  plants  or  colonies 
(Pleurococcus) ;  then  filamentous  plants  (  Ulothrix,  (Edogonium, 
Spirogyra);  then  branching  filaments  (Vaucheria,  Cladopliora) ; 
and  branching  filaments  with  leaf-like  expansions  (brown 
algae).  The  chloroplasts,  at  first  poorly  organized,  become 
definite  and  often  quite  complex  structures.  The  lowest  algae 
are  free-floating,  but  a  holdfast  develops  (  Ulothrix,  (Edogonium^ 
brown  and  red  algae)  which  gives  relative  permanence  of  liv- 
ing-place. Distinct  basal  and  apical  ends  and  the  branching 
habit,  with  well-organized  and  well-exposed  chloroplasts,  pro- 
vide a  favorable  organization  for  manufacture  of  foods. 

10nly  part  of  the  types  of  plants  that  have  been  discussed  in  this  text 
are  cited  in  this  summary. 


332  PRACTICAL  BOTANY 

The  green  algse  offer  the  best  series  in  evolution  of  repro- 
ductive organs.  One-celled  plants  that  reproduce  vegetatively 
(fission)  and  sometimes  by  zoospores  are  followed  by  plants 
which,  while  still  reproducing  vegetatively,  have  vegetative 
cells  which,  by  division  of  their  contents,  produce  numerous 
asexual  spores  (zoospores),  as  in  Cladophora  and  Ulothrix. 
From  small  zoospore-like  bodies  the  first  sex  spore  (zygospore) 
is  formed,  and  the  origin  of  gametes  and  sexuality  in  plants 
appears.  Then  in  (Edogonium  vegetative  cells  produce  special 
sex  organs  (oogonia  and  antheridia)  in  which  differentiated 
gametes  (eggs  and  sperms)  are  formed.  From  these  the  oospore 
is  formed.  In  such  cases  as  this  we  have  an  illustration  of  the 
differentiation  of  sex  cells  into  male  and  female,  and  the  dif- 
ferentiation of  sex  organs.  Finally,  in  plants  such  as  Vaucheria 
the  sex  organs  are  made  solely  for  reproductive  work. 

304.  Bryophytes.  This  division  is  subdivided  into  two 
classes,  liverworts  and  mosses.  The  protonema  of  mosses 
greatly  resembles  the  green  algse,  and  some  simple  liver- 
worts are  masses  of  cells  much  like  some  of  the  higher  algse. 
Rhizoids  and  special  chlorophyll  tissues  are  developed  both  in 
liverworts  and  in  mosses,  and  in  the  highest  members  of  each 
class  leaf-like  and  stem-like  structures  are  formed.  In  the 
mosses  this  leafy  plant  is  erect,  the  leaves  are  radially  arranged 
about  the  stems,  and  altogether  the  mosses  appear  to  be  good 
chlorophyll-working  plants.  While  the  liverworts  have  not 
developed  the  erect  stem  and  radially  arranged  leaves,  in  the 
leafy  liverworts  there  is  an  almost  equal  degree  of  vegetative 
differentiation.  The  chlorophyll  tissues  of  bryophytes  present 
a  great  advance  over  those  of  thallophytes. 

In  reproduction,  bryophytes  also  offer  distinct  advances  over 
thallophytes.  The  sex  organs  are  complex  structures.  The 
egg  is  produced  in  a  many-celled  archegonium,  instead  of  the 
one-celled  oogonium  of  the  thallophytes,  and  the  sperms  are 
produced  in  a  many-celled  antheridium.  These  organs  may 
be  embedded  in  the  thallus  or  borne  upon  the  surface.  The 
oospore  produces  a  distinct  phase  of  the  plant,  which  whea 


AHGtOSPEBMS  333 

mature  produces  asexual  spores.  This  gives  rise  to  alterna- 
tion of  generations,  in  which  a  gametophyte  by  means  of  an 
egg  and  a  sperm  produces  an  oospore ;  the  oospore  upon  ger- 
mination produces  a  sporophyte ;  the  sporophyte  produces 
asexual  spores,  which  germinate  and  produce  new  gameto- 
phytes.  In  some  bryophytes  (mosses  and  Anthoceros)  the  spo- 
rophyte bears  chlorophyll,  but  in  all  it  is  wholly  or  largely 
dependent  upon  the  gametophyte  for  nourishment.  The  game- 
tophyte is  the  chief  chlorophyll-working  generation.  Indeed, 
the  most  complex  nutritive  structures  in  any  gametophyte  of 
the  plant  kingdom  are  in  the  bryophytes. 

305.  Pteridophytes.  In  most  pteridophytes  both  generations 
bear  chlorophyll.  In  the  true  ferns  the  gametophyte  is  smaller 
and  less  complex  than  in  most  bryophytes.  It  looks  like  n 
simple  liverwort.  The  sporophyte  has  a  heavy  woody  stem 
and  large  leaves.  The  stem  and  leaves  possess  fibrovascular 
tissues,  which  aid  in  giving  support  and  in  conducting  food 
material.  The  introduction  of  fibrovascular  tissue  represents 
an  epoch  of  very  great  significance  in  the  plant  kingdom.  It 
makes  possible  the  development  of  large  upright  plants  and 
giant  tree  trunks,  which  can  expose  chlorophyll  tissue  high  in 
the  air.  It  must  be  kept  in  mind  that  in  so  far  as  bryophytes 
develop  special  chlorophyll  structures,  these  are  found  in  the 
gametophyte  and  not  in  the  sporophyte. 

In  the  true  ferns  a  gametophyte  may  bear  both  sex  organs 
and  produce  an  oospore.  The  sporophyte  produces  many  spores, 
any  of  which  may  produce  gametophytes.  The  asexual  spores 
are  of  one  kind  (homosporous).  In  other  fern-like  plants 
(^Selaginella)  two  kinds  of  asexual  spores  (heterosporous)  are 
produced.  The  small  spores  produce  male  gametophytes,  which 
produce  the  antheridia  and  sperms,  and  the  large  spores  pro- 
duce female  gametophytes,  which  produce  archegonia  and  eggs. 
The  egg  is  fertilized  within  the  female  gametophyte,  which 
has  not  escaped  from  the  megaspore  wall.  The  oospore  pro- 
duces an  embryo  sporophyte,  which  grows  out  of  the  old 
megaspore  wall,  and  becomes  established  as  a  new  plant. 


334  PRACTICAL  BOTANY 

A  period  of  dormancy  after  the  embryo  is  formed  would  cause 
the  old  megaspore  and  its  contents  (female  gametophyte  and 
embryo)  to  look  much  like  the  seed  of  spermatophytes. 

306.  Spermatophytes.  The  sporophyte  of  the  seed  plants 
is  a  far  better  nutritive-working  plant  than  those  of  any  of 
the  preceding  divisions.  Not  only  has  it  better  structures 
for  making  food,  but  many  structures  and  habits  enable  these 
plants  to  store  surplus  food  from  more  active  through  less 
active  periods,  or  from  year  to  year. 

From  an  evolutionary  point  of  view  the  seed  marks  the  most 
important  advance  in  the  spermatophytes.  The  seed  is  the 
megasporangium  (ovule)  and  the  remaining  part  of  the  female 
gametophyte  and  the  embryo  sporophyte.  It  can  lie  dormant 
through  unfavorable  periods,  often  for  years,  and  upon  return 
of  favorable  conditions  proceed  to  grow.  Its  stored  food 
nourishes  the  young  plant  until  it  establishes  its  own  food- 
making  structures. 

In  gymnosperms  the  megasporangium  (ovule)  and  the  seed 
which  is  developed  from  it  are  borne  upon  the  megasporophyll 
and  not  within  it,  as  in  angiosperms.  In  the  first  case  the 
microspore  (pollen  grain)  alights  upon  the  ovule.  A  pollen 
tube  carries  the  male  cells  or  sperms  to  the  egg.  In  angio- 
sperms the  pollen  grain  alights  upon  the  stigma  of  the  carpel. 
The  pollen  tube  carries  the  male  cells  through  the  style  to  the 
ovule,  thence  through  it  to  the  egg.  In  the  gymnosperms  the 
female  gametophyte  is  developed  from  the  megaspore  entirely 
within  the  ovule,  is  composed  of  many  cells  compactly  arranged, 
and  bears  archegonia  and  eggs.  In  the  angiosperms  the  female 
gametophyte  is  not  compact,  is  reduced  to  seven  cells,  and 
bears  an  egg  without  a  surrounding  archegonium.  Further- 
more, this  angiosperm  gametophyte  has  a  second  period  of 
growth,  which  results  in  production  of  the  endosperm  of 
the  seed. 

In  spermatophytes  the  gametophytes  are  very  nearly  lost.  They 
are  so  inconspicuous  that  they  are  hard  to  understand,  but  they 
cannot  be  wholly  lost  while  plants  have  sexual  reproduction. 


CHAPTER  XX 

SOME    LEADING    FAMILIES    OF    FLOWERING    PLANTS    AND 
THEIR  USES1 

MONOCOTYLEDONS 

307.  Introductory.  When  people  speak  of  flowering  plants 
they  usually  mean  angiosperms,  or  plants  with  a  closed  ovary 
(Fig.  101),  including  all  the  families  of  monocotyledons  and 
dicotyledons.  As  shown  in  Sects.  302-306,  these  groups  oc- 
cupy the  highest  place  in  the  plant  world. 

Monocotyledonous  plants  usually  have  seeds  with  one  coty- 
ledon, flowers  with  their  parts  in  threes,  leaves  with  parallel  vein- 
ing  (Fig.  268),  and  stems  with  the  woody  bundles  not  forming  a 
hollow  cylinder  about  a  central  pith  (see  Fig.  38).2 

Dicotyledonous  plants  usually  have  flowers  with  their  parts 
mostly  in  fives  (not  in  threes),  seeds  with  two  cotyledons,  leaves 
with  netted  veining  (Fig.  270),  and  stems  with  the  woody  bundles 
arranged  at  first  in  a  hollow  cylinder  about  a  central  pith  (see 
Fig.  30).3 

1  TEACHERS'  NOTE.  There  is  included  in  this  chapter  a  great  deal  of  infor- 
mation about  the  families  presented  and  their  economic  value.    Generally  it 
will  not  be  found  advisable  to  use  the  entire  chapter  as  a  basis  for  assigned 
lessons.   Sometimes  it  should  be  so  used,  but  more  often  it  will  be  found  val- 
uable for  collateral  reading  and  as  a  source  of  information  regarding  many 
questions  that  arise  in  an  elementary  course.    A  few  figures  of  plants  from 
families  not  mentioned  in  the  text  have  been  introduced  for  the  sake  of 
illustrating  additional  types. 

2  There  are  occasional  exceptions  to  these  statements  ;  for  instance,  most 
seeds  of  the  Orchis  family  have  no  cotyledon,  the  pondweeds  (Potamogeton) 
have  flowers  with  parts  in  fours,  the  leaves  of  Trillium,  Smilax,  jack-in-the 
pulpit,  and  plants  of  the  Yam  family  are  netted-veined. 

3  A  few  dicotyledons,  like  Cyclamen,  have  seeds  with  only  one  cotyledon, 
and  a  few  others,  like  Indian  pipe  (Monotropa),  have  no  cotyledons.    Some 
parasites  have  hardly  any  stem,  but  are  practically  flowers  attached  to  the 
root  or  stem  of  the  host  by  numerous  haustoria. 

335 


336 


PEACTICAL  BOTANY 


308.  Families  of  monocotyledons.  There  are  about  forty 
families  of  monocotyledons,  variously  grouped  by  botanists  into 
from  seven  to  eleven  orders,  and  embracing 
over  20,000  species.  This  chapter  will  discuss 
only  four  of  the  most  important  families,  —  the 
Grass  family  (Grraminece),  the  Palm  family 
(Palmce),  the  Lily  family  (lAliacece),  and  the 
Orchis  family  (Orchidacece). 

309.  The  Grass  family.  The  grasses  num- 
ber about  3500  species,  and  are  distributed 
very  widely  over  the  earth's  surface.  Some 
species,  such  as  the  wild  rice  found  in  the  Mid- 
dle West  and  northward,  are  aquatic,  others 
grow  in  semi-desert  regions ;  but  most  grasses 
inhabit  plains,  meadows,  or  open  woods.  Tree- 
like species,  such  as  the  bamboos  of  many 
kinds,  may  form  dense  and  lofty  groves,  and 
our  Southern  canebrakes  are  tall  and  almost 
impenetrable;  on  the  other 
hand,  the  smallest  of  the 
grasses  are  of  sparse  growth 
and  only  a  few  inches  in 
height.  Grasses  are  generally  gregarious ; 
that  is,  many  individuals  of  a  species  grow 
side  by  side.  It  is  rarely  that  a  single  plant 
occurs  without  neighbors  like  itself.  The 
general  form  and  appearance  of  the  ordi- 
nary grasses,  with  their  usually  hollow  and 
conspicuously  jointed  stems,  are  familiar  to 
all.  The  flowers  are  rather  small,  and  rela- 
tively simple  (Figs.  271  and  272) ;  the  struc- 
ture of  the  fruit  and  seed  is  sufficiently 
shown  in  Figs.  128  and  129. 

310.  Various  uses  of  the  grasses.  The  Grass  family  is  proba- 
bly more  useful  to  man  than  any  other  family  of  plants.  Tlie 
bamboo  serves  the  Asiatic  peoples  among  whom  it  grows  for 


FIG.  268.  Paral- 
lel-veined leaf  of 
canna,veins  run- 
ning from  mid- 
rib to  margin 


FIG.  269.    Parallel- 
veined  leaf  of  Solo- 
mon's seal 
After  Strasburger 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     337 


many  of  the  purposes  for  which  we  employ  wood,  various 
fibers,  earthenware,  and  metals.  It  is  almost  the  only  material 
used  in  house  construction  and  in  bridge 
building ;  it  is  used  for  fences,  water  pipes, 
troughs,  jars,  mats,  baskets,  and  miscel- 
laneous household  articles. 
Straw  of  many  kinds 
of  grains  is  braided  into 
mats,  baskets,  and  hats, 
and  is  much  used  in  mak- 
ing coarse  paper ;  it  is  also 
used  as  a  winter  food  for 
domestic  animals. 

Esparto,  a  very  tough, 
coarse  grass  imported  from 
Spain  and  the  North  Af- 
rican coast,  is  extensively 
used  in  paper-making  and 
for  stuffing  mattresses. 

Sugar  cane,  a  very  large 
solid-stemmed  grass  (Fig. 
273),  is  considerably  raised  in  Louisiana  and 
in  some  Southern  states,  and  more  extensively 
in  the  West  Indies,  Hawaii,  and  Java.  Once 
it  was  almost  the  only  source  of  commercial 
sugar,  and  it  still  furnishes  about  a  third  of 
the  world's  supply.  Its  growth  and  commercial 
use  have  been  an  important  factor  in  tropical 
industrial  life. 

Meadow  and  pasture  grasses  are  highly  im- 
portant to  man.  The  best  meadows  are  usu- 
ally carefully  sown  with  selected  seed,  but 
pastures  are  generally  self-sown  with  grasses 
of  many  kinds.  Most  of  the  grasses  valuable  for  haymaking 
or  for  pasture  grow  best  in  northern  climates,  with  moderate 
summer  temperature  and  abundant  rainfall.  This  fact  makes 


FIG.    270.    Pinnately 

netted-veined  leaf  of 

foxglove 


FIG.  271.  Spike- 
like   panicle   of 

vernal  grass 
(Anthoxanthum) 

a, mature  anthers. 
Slightly  enlarged 


338 


PRACTICAL  BOTANY 


it  difficult  to  grow  hay  to  the  best  advantage  or  to  maintain 
good  pastures  in  the  South  or  (without  irrigation)  in  the  arid 
portion  of  the  Great  Plains. 

The  grasses  most  valuable  for  hay,  like  timothy  and  redtop, 
are  those  which  grow  rather  tall  and  contain  much  nutriment 
in  the  stem  and  leaves,  in  the  seeds,  or  in  both.  The  best  pas- 
ture grasses,  like  the  famous  Kentucky  blue  grass,  are  those 
which  spread  freely  by  rooting  branches  (stolons)  from  the 


a-— 


D 


FIG.  272.  Vernal  grass  (Anthoxanthum) 


A,  a  one-flowered  spikelet:  a,  b,  the  outer  empty  glumes.  B,  a  spikelet  with  the 
outer  glumes  removed:  e,  c,  the  inner  empty  glumes  (neuter  flowers),  with  long, 
bristle-shaped  appendages;  d,  e,  palets;  anth.,  anthers;  stig.,  stigmas.  C,  dia- 
gram of  cross  section  of  a  spikelet:  a,  glume;  d,  palet,  within  which  are  the  sta- 
mens and  pistil.  D,  a  fruit.  All  magnified.  After  Cosson  and  De  Saint-Pierre 

base,  and  which  finally  mat  together  to  form  a  compact  turf, 
not  easily  destroyed  by  trampling.  Their  nutritive  value 
must  also  be  high.  In  poor  soil  or  where  lack  of  moisture  or 
too  much  shade  makes  vigorous  growth  of  the  best  grasses 
impossible,  inferior  but  more  hardy  species  may  serve  a  useful 
purpose.1 

1  For  other  facts  about  common  grasses  consult  Chapter  XXIV.  See 
also  Warren,  Elements  of  Agriculture,  chap.  vii.  The  Macmillan  Company, 
New  York. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     339 

311.  The  cereal  grasses.  The  cereals,  or  grasses  cultivated 
for  their  edible  grains,  furnish  the  most  important  part  of  our 
vegetable  food  and  much  of  that  consumed  by  our  domestic 
animals  as  well.  The  principal  species  grown  in  ordinary 


FIG.  273.  A  field  of  sugar  cane  at  Vera  Cruz 
After  Freeman  and  Chandler 

soils  in  temperate  climates  are  wheat,  corn,  oats,  rye,  and 
barley.  Various  kinds  of  millet  much  used  as  human  food  in 
Asia  and  elsewhere  are  with  us  only  forage  crops.  The  rice 
plant  is  noteworthy  among  the  cereals  as  being  aquatic,— 
usually  cultivated  during  the  earlier  months  of  its  growth 
partially  or  wholly  under  water  (Fig.  274).  Some  details  in 
regard  to  the  cereals  will  be  found  in  Chap.  XXIV. 


FIG.  274.  Harrowing  flooded  ground  for  a  rice  field  in  Java  to  get  rid  of  the 

weeds 
After  Freeman  and  Chandler 


FIG.  275.  A  group  of  coco  palms 
Photograph  furnished  by  United  Fruit  Company 


340 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     341 

312.  The  Palm  family.  The  palms  number  about  1100 
species,  principally  tropical.  Most  of  the  familiar  palms  have 
a  nearly  cylindrical  trunk,  crowned  with  a  great  rosette  of 
pinnately  or  palmately  divided  leaves  (Fig.  275).  Many 


FIG.  276.  Flower  clusters  of  the  coco  palm 

The  upper  cluster  is  shown  at  an  early  stage,  with  the  staminate  flowers  still  cling- 
ing to  its  branches.  The  lower  cluster  has  lost  the  staminate  flowers  and  the  young 
coconuts  have  enlarged  considerably.  After  Freeman  and  Chandler 

palms  are  among  the  most  beautiful  plants,  and  no  other 
kind  of  tree  gives  such  a  tropical  air  to  a  landscape  in  which 
it  is  abundant.  Some,  such  as  the  rattan,  are  lianas,  with 
supple  stems  hundreds  of  feet  long.  The  flowers  are  not 
usually  very  conspicuous  and  are.  borne  ia  much-branched 


B 


FIG.  277.  Dragon-root,  a  plant  of  the  Arum  family,  a  monocotyledon  with 
netted-veined  leaves 

A,  entire  plant ;  t,  tuber ;  B,  the  flower  cluster  surrounded  by  a  hood-like  bract 

About  one  eighth  natural  size 

342 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     343 


inflorescences,  eacli  cluster  provided  with  a  very  large  bract 
(spathe),  shown  above  each  cluster  in  Fig.  276.  The  fruit  is 
often  a  berry,  as  in  the  date,  or  a  drupe,  as  in  the  coconut. 

313.  Uses  of  palms.  In  tropical 
countries  use  is  made  of  palm  wood 
and  the  leaves  in  various  kinds  of 
construction,  and  the  fruit  of  some 
kinds  (royal  palm)  is  used  as  food 
for  domestic  animals.  The  stems 
of  the  rattan  palm  are  largely 
employed  in  the  manufacture  of 
baskets  and  light  furniture.  The 
fiber  of  the  coco  palm  is  utilized 
in  making  coarse  matting  and 
heavy  cordage. 

Palm  oil,  much  used  in  soap 
making,  is  obtained  from  the  fruit 
of  the  African  oil  palm. 

The  coco  palm  (Figs.  275-276) 
ib  the  most  important  tree  of  the 
family.  It  grows  very  widely  dis- 
tributed along  tropical  coasts  and 
will  flourish  on  beaches  of  coral 
islands  where  no  other  valuable 
tree  can  be  made  to  grow.  The 
milk  of  the  unripe  nut  is  a  refresh- 
ing drink,  and  the  nuts  themselves 
are  largely  used  for  food  by  the  na- 
tives of  coconut-growing  regions. 
The  meat  (endosperm)  of  the  nut 
is  the  only  considerable  article  of 
export  from  many  islands  of  the 
South  Pacific.  It  is  sold  under  the 
name  of  copra  and  is  the  source  of 
coconut  oil.  As  is  well  known, 
the  nuts  are  largely  sold  in  our 


FIG.  278.  A  monocotyledonous 
plant,  the  spider  lily,  or  spider- 
wort  ( Tradescantia  virginica) 

One  sixth  natural  size 


344  PRACTICAL  BOTANY 

markets,  and  shredded  and  desiccated  coconut  finds  a  place 
in  the  preparation  of  candies  and  various  articles  for  the  table. 
The  date  palm  furnishes  one  of  the  most  considerable  arti- 
cles of  food  for  the  peoples  of  northern  Africa  and  western 
Asia.  It  has  been  in  cultivation  for  as  much  as  four  thousand 
years  and  there  are  several  thousands  of  named  varieties.  It  is  a 
most  productive  tree,  bearing  for  a  century  or  more,  and  when 
well  grown  producing  from  100  to  600  pounds  of  fruit  a  year. 


FIG.  279.  Trillium 

A  shade  plant  of  the  Lily  family,  which  hlossoms  before  the 
trees  beneath  which  it  grows  are  in  leaf 

Vigorous  and  successful  attempts  are  now  under  way  to 
introduce  date  culture  into  the  United  States.1  A  very  hot, 
dry  climate  is  required,  as  the  late  varieties  demand  a  mean 
temperature  of  90°  F.  for  three  months  of  the  year.  It  is 
important  to  secure  a  moist  soil  (by  irrigation  if  necessary) 
for  date  culture.  A  large  region  of  central  Arizona,  the  Colo- 
rado desert  in  California,  and  several  other  arid  or  semi-arid 
areas  will  probably  be  found  adapted  to  this  industry,  and 
dates  have  already  been  successfully  grown  in  some  portions 
of  this  region. 

1  See  Yearbook  of  the  Department  of  Agriculture,  1900. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     345 


314,  The  Lily  family  (Lffi- 
The  Lily  family  num- 
bers about  2600  species. 
These  are  scattered  over 
most  parts  of  the  world. 
They  are  especially  abundant 
in  regions  with  a  long  dry 
season,  like  South  Africa, 
the  Mediterranean  countries, 
and  parts  of  California.  Most 
Liliacece  are  herbs,  though 
a  few  are  shrubs  or  small 
trees.  Many  species,  like  the 
lilies  and  tulips,  have  bulbs 
which  survive  the  winter  or 
a  dry  season,  while  the  rest  of 
the  plant  dies  to  the  ground 
every  year.  Others,  as  the 
lily  of  the  valley  and  Sol- 
omon's seal,  spring  from  the 
rootstocks  (Fig.  60),  and  still 
others,  as  the  yucca  and  as- 
paragus, have  mainly  fibrous 
roots.  The  flowers  are  hy- 
pogynous,  often  showy,  and 
the  parts  of  the  perianth  fre- 
quently all  alike  or  nearly  so. 
The  structure  of  a  typical 
seed  is  shown  in  Fig.  127. 

Ornamental  plants  of  the 
Lily  family  are  among  the 
commonest  in  cultivation. 
Familiar  examples  are  the 
true  lilies,  the  hyacinths,  the 
star  of  Bethlehem,  squill,  tu- 
lip, crown  imperial,  day  lily, 


FIG.  280.  White  dogtooth  violet 

A  common  plant  of  the  Lily  family,  with  the 
stem  springing  from  a  deeply  buried  bulb. 
The  dotted  line  shows  how  much  of  the  plant 
was  underground.  About  half  natural  size 


FIG.  281.  The  stemless  lady's-slipper  (Cypripedium  acaule) 
One  of  the  most  familiar  orchids  of  the  northeastern  states 


340 


LEADING  FAMILIES  OF  FLOWEKING  PLANTS     347 


and  lily  of  the  valley.  Showy  wild  genera  are  the  following: 
many  lilies,  the  dogtooth  violet  (Fig.  280),  Trillium  (Fig.  279), 
Clintonia,  and  several  Rocky  Mountain  and  Pacific  coast  genera, 
such  as  Brodicea  and  Calochortus. 

Useful  plants  are  not  very  numerous  in  the  Lily  family. 
Asparagus  and  onions  are  common  articles  of  food.  Colchicum, 
Veratrum,  Aloe,  Smilax,  and  a  few  other  genera  yield  valua- 
ble medicines.  The  so- 
called  New  Zealand  flax 
produces  an  important 
fiber. 

315.  The  Orchis  fam- 
ily (Orchidacee).  The 
orchids  number  more 
than  5000  species  dis- 
persed throughout  trop- 
ical, sub-tropical,  and 
temperate  climates.  Few 
other  plants  seem  as  ca 
pricious  in  their  distri- 


bution, since  a  single 
individual  or  a  small 
patch  of  them  may  con- 


stig 


FIG.  282.  Lengthwise  section  of  one  of  the 

flowers  of  Fig.  281 

stig,  stigma;  sta,  imperfect  stamen  of  bract- 
Stitute    the    Ollly  repre-      ^e  appearance ;  a,  anthers  of  perfect  stamens ; 
, .  f  o,  ovary 

sentation  01   a   species 

throughout  a  considerable  region.  Orchids  are  all  herbs,  but 
vary  greatly  in  habit,  from  low  forms  with  hardly  any  stem 
aboveground,  —  like  the  true  Orchis  and  the  lady's-slipper 
(Cypripedium)  (Figs.  281  and  282),  —  to  tall  climbers  like  the 
vanilla  plant  and  such  air  plants  as  Fig.  20.  Some  genera, 
like  the  coralroot,  are  almost  or  quite  destitute  of  chlorophyll, 
and  live  as  root  parasites  or  as  saprophytes.  Many  species 
have  tubers  and  are  able  to  survive  a  long  dry  season.  The 
flowers  are  of  peculiar  forms  and  have  developed  the  most 
remarkable  known  structures  for  insect  pollination.  Great 
numbers  of  orchids  are  cultivated  in  greenhouses,  and  are 


348  PRACTICAL  BOTANY 

among  the  most  admired  and  highly  prized  of  all  ornamental 
plants.  The  only  important  useful  orchid  is  the  vanilla  plant, 
a  native  of  Mexico  and  the  West  Indies,  from  the  unripe  pods 
of  which  vanilla  is  obtained. 

316.  Useful  products  from  other  families.  Many  families  of 
monocotyledons  yield  single  products  of  much  value.  A  few 
of  the  most  important  of  these  useful  products  are  as  follows  : 


FIG.  283.  Fruiting  pineapple  plants,  Natal,  South  Africa 
After  Freeman  and  Chandler 

Fibers  are  secured  from  the  Sedge  family  (genus  Cyperus), 
—  used  in  making  East  Indian  and  Chinese  mattings, — rfrom 
the  Amaryllis  family,  and  from  the  Banana  family. 

Edible  roots  and  rootstocks  are  derived  from  the  Yam  family 
and  the  Ginger  family. 

Fruits  of  great  value  are  produced  by  the  Pineapple  family 
(Fig.  283)  and  the  Banana  family.  Of  these  fruits  the  banana  is 
so  important  an  article  of  food  that  some  details  may  be  given 
in  regard  to  its  mode  of  growth  and  its  place  in  our  markets. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     349 

The  banana  plant  (Fig.  284)  is  herbaceous,  though  in  the 
most  favorable  soil  and  climate  it  may  reach  a  height  of  forty 
feet.  The  leaves  grow  to  be  as  much  as  ten  feet  long  and  two 
feet  wide,  and  are  usually,  when  full-grown,  slit  into  strips  by 
the  wind.  The  fruit  (technically  a  berry)  is  produced  in  long 
spikes,  each  bearing  a  hundred  or  more  bananas.  As  a  result 


FIG.  284.  Gathering  bananas  in  Costa  Rica 
Photograph  furnished  by  United  Fruit  Company 

of  long  cultivation  the  fruit  has  become  seedless,  and  the  plant 
is  propagated  by  suckers  from  the  base.  There  are  two  edible 
species,  running  into  about  176  varieties,  cultivated  every- 
where in  the  tropics  for  their  fruit.  Another  species,  grown  in 
the  Philippines,  is  an  important  fiber  plant,  yielding  "  Manila 
hemp." 

The  annual  imports  of  bananas  into  the  United  States  now 
amount  to  about  40,000,000  bunches,  while  in  1872  the  total 


350  PKACTICAL  BOTANY 

importation  was  only  about  500,000  bunches.  A  few  bananas 
are  grown  in  the  Gulf  States,  but  our  main  supply  comes  from 
Jamaica  and  Central  America.  Entire  trainloads  of  bananas 
are  shipped  daily  from  New  Orleans  and  Mobile  to  supply  the 
region  west  of  the  Mississippi  as  far  as  the  extreme  northwest, 
and  also  some  portions  of  the  country  east  of  the  Mississippi. 
Bananas  differ  from  ordinary  fruits  in  that  they  possess  a 
much  higher  nutritive  value,  so  that  they  constitute  a  true 
food  which  needs  little  supplementing  to  support  life  indefi- 
nitely. They  contain  about  three  times  as  much  protein  and 
one  and  a  half  times  as  much  carbohydrates  as  do  apples ;  in 
fact,  a  banana  has  about  the  same  food  value  as  a  potato,  con- 
taining two  thirds  as  much  protein  and  a  somewhat  larger 
quantity  of  carbohydrates. 

DICOTYLEDONS,  CHORIPETALOUS  SUB-CLASS 

317.  Families  of  dicotyledons.   There  are  about  34  orders 
of  dicotyledons,  comprising  200  or  more  families.    Of  these 
orders  26  belong  to  the  choripetalous  sub-class  and  8  to  the 
sympetalous  sub-class.    The  flowers  of  the  choripetalous  sub- 
class have  either  no  perianth,  or  one  consisting  of  separate 
sepals  and  petals  (or  sometimes  of  sepals  only).    The  flowers 
of  the  sympetalous  sub-class  have  a  sympetalous  corolla, 

In  this  book  only  five  of  the  most  important  among  our 
families  of  deciduous  trees  can  be  mentioned.  Some  other 
facts  in  regard  to  them  will  be'  found  in  Chapter  XXII. 
Four  of  the  other  principal  families  will  be  briefly  treated 
here,  —  namely,  the  Rose  family  (Rosaceoe),  the  Pea  family 
(Leguminosce),  the  Spurge  family  (JEuphorbiacece),  and  the 
Parsley  family  (Umbelliferce). 

318.  Some  families  of  hardwood  trees.    A  large  part  of  our 
valuable  hard  wood  comes  from  trees  of  four  families,  —  that 
of  the  willows  and  poplars,  that  of  the  walnuts  and  hickories, 
that  of  the  oaks,  chestnuts,  and  beeches,  and  that  of  the  elms. 
All  of  these  except  the  Elm  family  have  unisexual  flowers 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     351 


(Fig.  285),  often  one  or  both  kinds  in  catkins.  In  the  Elm 
family  (Fig.  286)  the  flowers  are  usually  bisexual.  A  fifth 
family,  that  of  the  mulberries,  includes  among  the  economic 
plants  of  temperate  North  America  few  except  the  mulberries 
and  the  Osage  orange,  the  hemp  and  the  hop.  This  family  also 
embraces  the  tropical  breadfruits,  and  the  great  fig  genus  of 


.E 


FIG.  285.  Gray  birch  (Betula  populifolia) 

A,  catkins,  natural  size :  s,  staminate ;  p,  pistillate.   B,  cluster  of  ripened  fruits ; 

C,  bract  with  three  staminate  flowers ;  D,  bract  with  three  pistillate  flowers ;  E, 

fruit.  B,  C,  D,  E,  somewhat  magnified 

some  600  species,  including  the  edible  fig  and  the  rubber  tree 
(Ficus  elastica). 

Edible  seeds  of  many  kinds  are  produced  by  members  of  the 
families  of  catkin-bearing  trees.  Most  familiar  are  the  Ameri- 
can and  the  European  walnuts,  the  hickory  nut,  and  the  pecan. 
Hardly  less  so  are  the  American  and  the  European  chestnuts. 

Edible  fruits — not  however  of  much  importance — are  borne 
by  the  mulberries.  The  breadfruit,  from  a  tree  of  the  same 


352 


PRACTICAL  BOTANY 


family,  forms  most  of  the  subsistence  of  many  islanders  of  the 
South  Pacific.  Figs,  belonging  to  the  Mulberry  family,  are  a 
highly  prized  article  of  food  in  their  native  countries.  They 
are  among  the  most  valuable  of  our 
imported  dried  fruits,  and  are  coming 
to  be  extensively  grown  in  California. 


D 


FIG.  286.  European  elm  (Ulmus  campestris) 


A,  a  flowering  twig;  B,  a  flower;  (7,  longitudinal  section  of  a  flower;  D,  a  fruit. 
A,  D,  natural  size ;  B,  C,  enlarged.   After  Wossidlo 


FIG.  287.  Pistils  in  the  Rose  family 

A,  Primus  type ;  B,  Potentilla  type ;  (7,  Rosa  type ;  c,  calyx ;  o,  ovary. 
After  Prantl 

319.  The  Rose  family  (Rosaces).  The  Rose  family  numbers 
about  2000  species  of  herbs,  shrubs,  and  trees.  The  flowers 
are  perigynous  or  epigynous  (Fig.  287),  with  the  parts  of  the 
perianth  usually  in  fives ;  stamens  generally  more  numerous 
than  the  divisions  of  the  perianth ;  carpels  one  to  many.  The 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     353 


fruit  is  dry  in  some  genera  (Fig.  147)  and  fleshy  in  others 
(Fig.  148).  Our  genera  are  grouped  into  four  divisions  (based 
on  characters  of  the  flowers  and  fruit),  which  are  often  ranked 
as  separate  families. 

320.  Various  uses  of  rosaceous  plants.  Aside  from  their  im- 
portance as  fruit  producers  (Chapter  XXIV),  plants  of  the 
Rose  family  are  of  value  in  many  other  ways. 

Medicinal  products  are  oil  of  bitter  almonds,  blackberry-root 
bark,  wild-cherry  bark,  and  oil  of  rose  (used  mainly  as  a  perfume). 

Cabinet  wood  of 
fine  quality  is 
furnished  by  our 
wild  black  cherry, 
and  the  wood  of 
the  apple,  pear, 
and  wild  haw- 
thorn is  excellent 
for  tool  handles 
and  similar  uses. 

In  the  Rose 
family  ornamental 
plants  are  so  nu- 
merous that  a 
mere  list  of  all  of 
them  would  oc- 
cupy too  much  space.  Some  of  the  principal  ones  are  roses, 
hawthorns,  various  species  of  spiraea,  several  kinds  of  crab 
apple,  the  rowan  tree  or  mountain  ash,  and  the  Japan  quince. 

321.  The  Pea  family  (Leguminosct).1   The  Pea  family  com- 
prises about  7000  species  of  herbs,  shrubs,  and  trees.    The 
flowers  are  usually  hypogynous  or  somewhat  perigynous,  often 
bilaterally  symmetrical  (Fig.  289),  perianth  generally  in  fives, 
pistil  of  one  carpel,  fruit  usually  a  one-celled  pod  (Fig.  290). 

1  The  characteristic  pod  of  the  family  is  called  a  legume,  and  the  plants 
of  the  most  familiar  of  the  sub-families  are  often  spoken  of  as  legumes,  but 
the  name  does  not  seem  to  be  botanically  desirable. 


FIG.  288.  Pea  family 

A,  actinomorphic  corolla  (Acacia  cinerascens) ;  B,  zygo- 

morphic  corolla  of  wild  senna  (Cassia  marilandica) . 

After  Schnizlein 


354 


PRACTICAL  BOTANY 


The  Leguminosce  constitute  the  largest  family  of  choripetalous 
dicotyledons,  an  extremely  important  one  on  account  of  the 
numerous  useful  species.  The  genera  are  divided  into  three 


FIG.  289.    Pea  family.    Papilionaceous  zygomorphic  corolla  of  sweet  pea 
(Lathyrus  odoratus) 

A,  side  view.  B,  front  view :  s,  standard ;  w,  w,  wings ;  k,  keel 

sub-families  (often  ranked  as  families),  of  which  the  acacia, 
the  redbud  (also  the  wild  senna),  and  the  sweet  pea  are  respec- 
tively well-known  types  (see  Figs.  288  and  289). 

322.  Edible  seeds  of  the  Pea  family.  Many  seeds  which  form 
an  important  part  of  human  food  are  derived  from  this  family. 
The  ones  most  generally  used  in  our  own  country  are  peas 
and  beans.  Peanuts  are  the  seeds  of  a  leguminous  plant  largely 


FIG.  290.  Pea  family.    Stamens  and  pistil ;  fruit 

A,  stamens  and  pistil  of  sweet  pea  (magnified) ;  B,  fruit;  C,  part  of  fruit, 
showing  one  seed 

grown  in  the  South  Atlantic  states  and  elsewhere,  which  forces 
its  pods  underground  to  ripen.  Our  crop  of  4,000,000  or  more 
bushels  per  year  is  largely  consumed  at  home,  but  is  also  con- 
siderably exported. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     355 


Other  leguminous  seeds  much  used  as  articles  of  food  in 
Europe,  though  not  much  eaten  in  the  United  States,  are 
broad  beans,  chick-peas,  and  lentils. 

323.  Other  useful  products  of  the  Pea  family.    Medicinal 
substances,  dyestuffs,  and  varnishes  are  obtained  from  several 
genera  of  leguminous  plants.    Among  the  most  familiar  of 

these  are  gum 
arabic,  licorice, 
balsam  of  tolu, 
senna,  catechu, 
tamarinds,  logwood,  and 
copal  varnish. 

Timber  of  considera- 
ble value  for  some  pur- 
P°ses  is  Stained  from 
two  North  American 
genera,  the  black  locust 
and  the  honey  locust. 
Rosewood,  blackwood, 
ironwood  (Afzelia),  cor- 
alwood,  and  some  other 
kinds  used  in  fine  cab- 
inet work,  are  from 
tropical  or  sub-tropical 
leguminous  trees. 

324.  Ornamental  leguminous  plants.  The  list  of  ornamental 
plants  of  the  Leguminosce  is  a  very  long  one.    Many  genera, 
such  as  the  true  acacia,  are  not  hardy  in  the  Northern  states, 
but  a  large  number  of  our  familiar  cultivated  herbs,  shrubs, 
and  trees  are  leguminous  plants.   Among  the  herbaceous  ones 
are  lupines,  sweet  clover,  scarlet  runner,  the  sweet  pea  and 
a  scentless  species  which  much  resembles  it.    Common  shrubs 
are  several  acacias,  the  "  genista  " l  of  the  florists,  "  rose  aca- 
cia," and  wisteria.    Commonly  planted  trees  are  the  black 
locust,  honey  locust,  yellowwood,  and  laburnum. 

1  Cytisus  canariensis. 


FIG.  291.  Desmodium  flowers  and  fruit 
An  herb  of  the  Pea  family.  Reduced 


356 


PRACTICAL  BOTANY 


325.  The  Spurge  family  (Euphorbiacea*).  The  Spurge  family 
comprises  about  4000  species,  many  of  them  tropical.  The 
flowers  (Fig.  292)  are  hypogynous,  mostly  unisexual;  peri- 
anth usually  simple 
or  wanting;  stamens 
one  to  many;  ovary 
of  three  carpels  and 
three  locules,  with 
one  or  two  ovules  in 
each  locule.  Often 
the  inflorescence  is 
so  small  and  com- 
pact as  to  be  easily 

mistaken  for  a  flower  (Fig.  292).  The 
plants  of  the  Spurge  family  are  herbs, 
shrubs,  or  trees,  often  succulent  and  cactus- 
like,  usually  with  a  milky  juice,  which  in 
many  species  is  poisonous. 

326.  Useful  plants  of  the  Spurge  family. 
Several  species  of  this  family  yield  highly 
valuable  products. 


FIG.  292.  I,  Euphorbia  splendens ;  II,  Euphorbia  corollata 

.A,  flower  cluster  with  involucre,  the  whole  appearing  like  a  single  flower.  7?,  a 
single  staminate  flower:  a,  anther.  C,  fertile  flower,  as  seen  after  the  removal 
of  the  sterile  flowers.  D,  partly  matured  fruit,  i,  involucre ;  s,  stigmas ;  c,  capsule 

The  cassava  plant  is  a  native  of  Brazil  but  is  now  cultivated 
in  many  of  the  warmer  parts  of  the  world,  including  our  own 
Gulf  States.  Tapioca  is  made  from  the  clustered  roots,  which 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     357 


from  a  single  plant  sometimes  weigh  as  much  as  thirty  pounds. 
The  ground  or  sliced  roots  are  largely  fed  to  horses,  cattle, 
and  hogs.  One  of  the  most  valuable  species  has  an  acrid  poi- 
sonous juice,  which  must  be  removed  by  heating  or  drying  the 
ground-up  roots  before  they  are  fed 
to  animals.. 

Medicinal  substances  in  considerable 
number  —  especially  cascarilla  bark, 
castor  oil,  and  croton  oil  —  are  ob- 
tained from  euphorbiaceous  plants. 

India  rubber  is  largely  obtained 
from  two  South  American  species  of 
Hevea,  a  plant  of  this  family  (Fig. 
293). 

Ornamental  plants  of  the  Spurge 
family  are  several  species  of  Euphor- 
bia (Fig.  292,  I),  one  of  them  com- 
monly known  as  Poinsettid,  and  the 
castor  bean^which  in  warm  climates 
grows  to  be  a  small  tree,  but  with  us 
is  a  large  annual. 

327.  The  Parsley  or  Carrot  family 
(  Umbettiferct) .  The  P  arsley  family  com- 
prises about  1300  species, — herbs 
which  are  mostly  natives  of  temper- 
ate regions  in  the  northern  hemi- 
sphere. The  structure  of  the  flowers 
and  fruit  can  be  understood  from 
Fig.  295.  As  the  flowers  are  usually 
much  alike,  the  distinctions  between  species  are  based  upon 
the  form  and  structure  of  the  fruit.  Many  species  have 
poisonous  qualities ;  some  —  as  the  poison  hemlock  (  Conium), 
asafostida,  anise,  and  coriander  —  have  medicinal  value.  The 
carrot,  parsnip,  celery,  and  fennel  are  of  considerable  impor- 
tance as  food  substances,  and  parsley  leaves  and  caraway  fruits 
("  seeds  ")  are  much  used  for  their  flavoring  qualities. 


FIG.  293.  Hevea  tree  tapped 
for  India  rubber 

After  Freeman  and  Chandler 


FIG.  294.    Ginseng  (Panax  quinquefolium),  a  plant  of  the  Ginseng  family, 

closely  related  to  the  Parsley  family.   It  is  used  in  Chinese  medicine,  and  is 

a  valuable  article  of  commerce 

A,  entire  plant;  £,  flower  cluster,  flower,  and  fruft 
358 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     359 

328.  Useful  products  from  other  families ;  foods  and  medi- 
cines. Valuable  products  are  obtained  from  many  other  fami- 
lies of  choripetalous  dicotyledons  besides  those  above  described, 
and  a  few  of  these  may  be  mentioned  in  this  place. 

Edible  fruits.  From  the  Saxifrage  family  we  get  currants 
and  gooseberries.  From  the  Rue  family  are  obtained  the 


FIG.  295.  Flower  and  fruit  of  Parsley  family  (Umbelliferce) 

A-D,  caraway  (Carum  Carvi):  A,  flower;  J5,  partly  matured  pistil;  C,  mature 

fruit ;  D,  cross  section  of  fruit.   E,  fruit  of  parsnip ;  F,  fruit  of  carrot,   c,  carpels ; 

cp,  carpophore,  or  stalk  to  which  ripe  carpels  are  attached ;  d,  disk ;  o,  oil  tubes; 

ov,  ovary ;  s,  stigmas.   A-D,  after  Schnizlein ;  E,  after  Bischoff 

citrous  fruits,  including  ordinary  oranges,  tangerines,  man- 
darins, lemons,  and  grapefruit. 

Of  the  Grape  or  Vine  family  only  one  genus,  the  grape,  is 
of  economic  importance,  but  it  is  an  old  and  very  important 
cultivated  plant. 

Chocolate  and  tea.  Chocolate  is  manufactured  from  the  seeds 
of  the  cacao  tree ;  this  tree  was  originally  found  in  Mexico, 
but  is  now  cultivated  in  hot  climates  in  many  parts  of  the 


360  PRACTICAL  BOTANY 

world.  The  flowers  spring  from  the  trunk  and  older  branches, 
and  mature  into  juicy,  many-seeded  fruits,  from  which  (after 
a  fermenting  process)  the  seeds  are  extracted,  roasted,  and 
ground.  The  family  to  which  the  cacao  tree  belongs  is  a  trop- 
ical one,  somewhat  related  to  the  familiar  Mallow  family. 

Tea  is  made  from  the  leaves  of  a  shrub  of  the  Tea  family 
(Fig.  296),  which  consists  of  tropical  and  sub-tropical  plants. 


FIG.  296.   An  American-grown  tea  bush,  from  Darjiling  seed 
(northern  India) 

The  bush  is  four  or  five  years  old,  and  has  been  plucked  for  the  tips  of  the  twigs, 

for  high-grade  tea.    Photograph  furnished  by  the  Bureau  of  Plant  Industry, 

United  States  Department  of  Agriculture 

The  tea  plant  is  thought  to  occur  in  a  wild  state  in  Assam, 
eastern  India,  and  has  certainly  been  cultivated  for  ages  in 
China  and  the  East  Indies.  The  tea  of  commerce  is  made 
by  drying  the  leaves  of  the  shrub,  allowing  them  during  the 
process  to  undergo  more  or  less  fermentation. 

Medicinal  and  other  products.  Opium  and  morphia  (which  is 
derived  from  opium)  are  obtained  from  capsules  of  the  opium 
poppy.  Cocaine  is  made  from  the  leaves  of  a  Peruvian  shrub, 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     361 


a  member  of  a  small  family  allied  to  the  geraniums.    Cinna- 
mon and  camphor  are  obtained  from  trees  of  the  Laurel  family. 

329.  Products  useful  in  textile  and  other  manufactures. 

Sumach  products.  From  shrubs  and  small  trees  of  the 
Sumach  family,  growing  in  the  United  States  and  in  Sicily, 
are  obtained  leaves  and  young 
twigs  much  used  for  tanning  the 
finer  kinds  of  leather. 

A  Japanese  species  of  sumach, 
with  very  poisonous  sap,  yields 
the  famous  Japanese  lacquer  so 
much  used  for  varnishing  articles 
of  wood  and  other  materials. 

Fiber  plants.  The  flax  plant, 
which  belongs  to  a  family  allied 
to  the  geraniums,  produces  from 
its  tough  bark  the  very  fine  and 
strong  fibers  from  which  linen 
goods  and  thread  are  made.  It 
is  grown  in  many  parts  of  Eu- 
rope, especially  in  Russia,  and 
somewhat  in  the  United  States, 
both  for  the  oil  obtained  from  its 
seeds  and  for  the  fiber. 

Valuable  fibers  or  hair-like  ma- 
terials are  yielded  by  plants  of 
three  closely  related  groups,  the 
Linden  family,  the  Mallow  family, 
and  the  Silk-cotton  family. 

Russian  bast  and  jute  are  products  of  the  Linden  family. 

Cotton,  the  most  important  fiber  plant,  is  discussed  at  some 
length  in  Chapter  XXIV. 

The  silky  fiber  sold  under  various  names  as  a  material  for 
stuffing  pillows,  cushions,  and  for  other  purposes,  is  obtained 
from  the  hairs  which  clothe  the  seeds  of  trees  of  the  Silk-cot- 
ton family  (Bombacaceoe),  a  small  family  of  tropical  plants. 


FIG.  297.  Flowers  of  papaw(^4si- 
mina  triloba) 

The  only  North  American  represent- 
ative of  the  tropical  Custard-Apple 
family,  noted  for  its  delicious  fruits 


362 


PRACTICAL  BOTANY 


330.  Ornamental  plants.  Only  a  very  few  of  the  best-known 
ornamental  plants  of  the  choripetalous  dicotyledons  not  already 
referred  to  can  here  be  mentioned.  Among  them  are  pinks, 

water  lilies,  lotuses, 
magnolias,  poppies, 
"  geraniums,"  "nas- 
turtiums "  (Tropceo- 
Imri),  balsams,  vio- 
lets, mallows,  be- 
gonias, and  cacti. 
Here  belong  a  large 
proportion  of  the 
annuals  in  our  gar- 
dens and  many  of 
the  familiar  early 
wild  flowers  of  the 
woods  and  fields, 
such  as  fire  pink, 
buttercup,  Dutch- 
man's-breeches,  he- 
patica,  anemone, 
catchfly,  and  blood- 
root.  Here,  too,  are 
classed  the  numer- 
ous showy  species 
of  the  Mustard 
family.  Many  fa- 
vorite shade  trees, 
such  as  the  oaks, 
birches,  elms,  and 
maples,  and  many  ornamental  shrubs,  such  as  barberries,  hollies, 
hibiscus,  and  others,  belong  to  the  choripetalous  sub-class.1 

1  Considerable  matter  relating  to  various  species  of  hard-wood  trees  (most 
of  which  are  choripetalous  dicotyledons)  will  be  found  in  the  summary  of 
facts  concerning  timber  in  Chapter  XXII,  and  a  short  account  of  the  citrous 
fruits  and  the  grapes  in  Chapter  XXIII. 


FIG.  298.  An  American-grown  camphor  tree 

The  tree  is  six  or  eight  years  old  and  eighteen  feet 
high ;  it  is  grown  on  the  Florida  "  high  pine  land,"  of 
almost  pure  white  sand.  Camphor-growing  is  now  car- 
ried on  extensively  in  this  region,  and  by  the  improved 
method  of  distilling  camphor  from  twigs  clipped  with 
their  leaves  from  the  live  tree  the  latter  is  little  in- 
jured, and  the  industry  can  be  carried  on  for  many 
years  without  replanting.  Photograph  furnished  by 
the  Bureau  of  Plant  Industry,  United  States  Depart- 
ment of  Agriculture 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     363 


DICOTYLEDONS;  SYMPETALOUS  SUB-CLASS 

331.  Families  discussed.  Five  sympetalous  families  will  here 
be  treated:  the  Heath  family,  the  Mint  family,  the  Nightshade 
family,  the  Madder  family,  and  the  Composite  family.    Not 
all  of  these  families  are  of  great 

economic  importance  (though  two 
of  them  are  so),  but  they  are  among 
the  best  representatives  of  sympet- 
alous plants,  —  the  highest  group 
of  the  vegetable  kingdom. 

332.  The  Heath  family  (Ericacea). 
This  family  numbers   over   1300 
species,  mostly  of  shrubs  or  under- 
shrubs,  widely  distributed  from  the 
polar  regions  to  the  tropical  forests. 
The  flowers  are  hypogynous  (Fig. 
90)  or  else  perigynous  (not  always 
sympetalous) ;  the  anthers  open  by 
pores  or  short  slits.    The  fruit  is  a 
capsule,  a  berry  (often  edible),  or 
a  drupe  with  very  small  seeds.  The 
leaves  are  generally  leathery  and 
evergreen,  often  small. 

333.  Important    plants    of    the 
Heath  family.    Cranberries,  blue- 
berries, and  huckleberries  are  highly 
valued  fruits  of  this  family.  Cran- 
berries are   borne   by  a  delicate, 
trailing,  woody  plant.  The  upland 

species  is  little  used,  but  the  ordinary  large  cranberry  (Fig. 
299),  found  in  peat  bogs  all  the  way  from  North  Carolina 
to  Minnesota  and  throughout  a  large  part  of  Canada,  is  much 
valued.  The  yield  from  uncultivated  bogs  is  considerable  ; 
in  Massachusetts,  New  Jersey,  and  Wisconsin  cranberries  are 
extensively  cultivated. 


FIG.  299.    The   common   cran- 
berry, not  quite  half  natural  size 


364  PRACTICAL  BOTANY 

Blueberries  and  huckleberries  belong  to  two  different  genera 
but  resemble  each  other  superficially.  The  former  berry,  borne 
on  bushes  of  several  species,  from  six  inches  to  ten  feet  in 
height,  is  the  more  valuable,  and  is  gathered  over  wide  areas 
of  the  northern  United  States  and  Canada.  The  "heaths," 
or  "  blueberry  barrens,"  on  which  the  bushes  grow  in  great 
abundance,  are  often  carefully  reserved,  to  be  picked  for 
the  market. 

Ornamental  shrubs  of  the  Heath  family  are  numerous  and 
highly  prized.  Best  known  among  them  are  the  rhododendrons 
(Fig.  56)  (including  many  species  commonly  called  azaleas) 
and  the  heathers.  The  so-called  mountain  laurel  (Kalmia)  is 
somewhat  cultivated,  and  is  a  characteristic  feature  of  many 
wooded  hill  and  mountain  sides  in  the  northeastern  states. 
The  "trailing  arbutus"  (Epigcea),  which  is  not,  properly  speak- 
ing, an  arbutus  at  all,  is  perhaps  the  favorite  spring  wild  flower 
of  those  regions  where  it  occurs.  The  madrono  (^Arbutus)  of  the 
Pacific  coast  is  one  of  the  most  beautiful  trees  of  that  region. 

334.  Mint  family  (Labiate).    This  family  comprises  about 
2600  species,  mostly  natives  of  warm  or  temperate  regions. 
The  flowers  are  hypogynous ;  stamens  usually  two  or  four ; 
ovary  f our-lobed,  with  a  single  style ;  corolla  bilaterally  sym- 
metrical.  Most  labiates  are  small  shrubs  or  herbs,  with  square 
stems  and  opposite  leaves ;  the  whole  plant  is  usually  aromatic 
and  often  glandular-hairy. 

For  so  large  a  family,  the  Labiatce  ranks  low  in  economic 
importance.  Many  species,  however,  afford  volatile  oils,  which 
are  of  use  in  medicine,  in  cookery,  or  for  perfumes.  Some 
beautiful  garden  plants  belong  to  this  family,  one  of  the  most 
familiar  being  the  scarlet  salvia. 

335.  The  Nightshade  family  (Solanacee).    This  important 
family  numbers  about  1300  species  common  in  warm  and 
temperate  regions.  The  flowers  are  hypogynous  ;  stamens  five ; 
ovary  two-loculed,  usually  many-ovuled ;  fruit  a  capsule  (Fig. 
300)  or  sometimes  a  berry.  Most  plants  of  the  family  are  herbs, 
but  some  shrubs  and  small  trees  occur,  especially  in  the  tropics. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     365 

Many  of  the  genera  are  actively  poisonous,  and  even  in  the 
case  of  edible  species,  like  the  potato,  the  foliage  and  other 
green  parts  often  have  an  offensive  smell  and  may  be  poisonous. 


FIG.  300.  Jimson  weed  (Datura) 

A  highly  poisonous,  ill-scented  weed  of  the  Nightshade  family,  common  in  barn- 
yards and  other  waste  ground.   A,  part  of  a  flowering  shoot;  B,  pod;  C,  cross 
section  of  pod.   One  half  natural  size 

336.  Three  important  plants  of  the  Nightshade  family. 
Three  solanaceous  plants  of  much  commercial  importance  are 
the  potato,  the  tomato,  and  tobacco.  The  potato  (Solatium 
tuberosum)  was  probably  introduced  into  cultivation  from 
Peru.  Its  tubers  have  long  formed  a  considerable  part  of 


366  PRACTICAL  BOTANY 

the  subsistence  of  mankind,  especially  in  the  cooler  parts  of 
Europe.  Potatoes  are  particularly  adapted  for  cultivation  as 
a  food  crop  in  regions  where  the  summer  is  so  short  and  cool 
that  wheat  or  Indian  corn  may  not  mature  or  produce  profit- 
able crops.  Many  varieties  have  been  produced  by  selection 
of  the  most  promising  plants  raised  from  the  seed  (collected 
from  the  berries  or  "  potato  balls  ").  Under  the  influence  of 
long  cultivation  the  size  of  the  tubers  has  greatly  increased 
(Fig.  331)  and  the  tendency  to  bear  seed  has  diminished. 

Our  annual  potato  crop  is  usually  over  200,000,000  bushels. 
New  York  is  the  principal  potato-growing  state,  producing 
nearly  twice  as  many  bushels  as  any  other  one  of  the  chief 
potato-producing  states,  Pennsylvania,  Michigan,  or  Wisconsin. 

The  tomato  (JLycopersicum  esculentum)  was  introduced  into 
cultivation  from  tropical  America,  at  first  as  a  curious  orna- 
mental plant  for  the  garden,  whose  fruit  was  supposed  to  be 
poisonous.  Its  fruit  was  originally  small,  two-celled,  and  wa- 
tery, but  by  cultivation  and  selection  has  become  large,  fleshy, 
and  several-celled.  It  is  extensively  grown  for  the  market, 
and  in  several  states  large  canning  establishments  handle  the 
product  of  many  special  tomato  farms. 

Tobacco  (Nicotiana  Tabacwri)  was  introduced  into  Europe 
from  America  during  the  latter  half  of  the  sixteenth  century. 
The  parent  form  of  the  cultivated  species  is  said  to  be  found 
in  the  wild  state  in  Peru  and  Ecuador.  Tobacco  is  an  ex- 
tremely profitable  though  somewhat  uncertain  crop.  It  im- 
poverishes the  soil  more  than  any  other  field  crop,  since  the 
plant  withdraws  from  it  great  quantities  of  nitrates.  The 
annual  product  of  the  United  States  and  Porto  Rico  amounts 
to  over  800,000,000  pounds,  the  leading  tobacco-producing 
states  being  Kentucky,  North  Carolina,  and  Virginia. 

337.  Other  important  genera.  No  other  plants  of  the  Night- 
shade family  are  of  great  v&lue  as  food  plants,  though  another 
species  of  Solanum,  the  eggplant,  is  considerably  cultivated. 
Red  peppers  {Capsicum),  ground  or  whole,  are  much  used  as 
a  condiment. 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     367 


Medicinal  substances  are  derived  from  belladonna,  Capsicum, 
Hyoscyamus,  and  other  solanaceous  plants. 

Ornamental  plants  of  this  family  are  rather  numerous.  The 
most  familiar  ones  are  species  of  Datura,  tobaccos  with  showy 
flowers,  matrimony  vine,  and  various 
species  of  Nierembergia,  Petunia,  and 
Salpiglossis. 

338.  The  Madder  family  (Rubiacea). 
This  is  one  of  the  largest  and  most 
diverse  families  of.  dicotyledons,  com- 
prising about  4500  species  of  herbs, 
shrubs,  and  trees.  Its  representatives 
occur  in  all  climates,  though  the 
majority  are  tropical.  The  flowers 
are  epigynous ;  calyx  minute ;  corolla 
lobes  and  stamens  as  many  as  the 
lobes  of  the  calyx;  ovary  with  two 
locules  ;  fruit  dry  or  fleshy.  The  out- 
line and  arrangement  of  the  leaves, 
—  which  are  almost  always  entire  and 
opposite, —  and  the  presence  of  leafy 
or  scale-like  stipules,  are  especially 
characteristic  of  the  family.  Our  com- 
monest wild  genera  are  three  herbs 
(bluets,  cleavers,  and  partridge  berry), 
and  also  one  shrub,  common  by  ponds 
and  river  banks,  —  the  buttonbush. 

Coffee  is  made  from  the  parched  seeds  of  a  small,  slender, 
evergreen  tree,  a  native  of  the  mountainous  portions  of  eastern 
Africa.  It  is  cultivated  in  many  warm  countries,  the  largest 
amount  coming  from  Brazil,  but  the  finest  quality  from  south- 
western Arabia  and  from  Java.  The  abundant  white  flowers, 
borne  in  axillary  clusters,  produce  red,  cherry-like  drupes 
(Figs.  301  and  302),  within  each  of  which  are  two  seeds,  the 
familiar  raw  coffee  of  commerce,  valued  for  the  caffeine  which 
they  contain  and  the  aromatic  oil  evident  after  roasting. 


FIG.  301.  A  coffee  twig  with 

berries 
After  Sadebeck 


368 


PRACTICAL  BOTANY 


Cinchona  trees  of  several  species,  growing  wild  in  the  Andes 
and  cultivated  in  India  and  elsewhere,  furnish  cinchona  bark. 
From  this  quinia  (quinine),  one  of  the  most  valuable  of  all 
remedies,  is  extracted. 

Ornamental  plants  of  two  genera  of  the  Madder  family  — 
Bouvardia  and  Gardenia  —  are   rather  commonly  cultivated 
in  greenhouses. 

339.  The  Composite  family  (Composite).  This  immense  fam- 
ily comprises  about  11,000  species,  those  of  temperate  climates 
mostly  herbs ;  some  species  of  the  tropics 
are  shrubs,  lianas,  and  even  trees.  The 
flowers  are  epigynous  (Fig.  303,  D)  ; 
calyx  rudimentary ;  corolla  tubular  and 
five-lobed,  or  strap-shaped,  or  bilaterally 
symmetrical ;  stamens  five,  with  anthers 
united  into  a  ring ;  stigma  two-lobed ; 
fruit  an  akene  (Fig.  304).  The  most 
obvious  characteristic  of  the  Compositce 
is  the  grouping  of  the  flowers  into  a 
head.  This  sometimes  (as  in  the  thistles) 
consists  wholly  of  tubular  flowers,  some- 
times (as  in  the  sunflowers  and  the  yar- 
row, Fig.  303)  of  tubular  disk  flowers 
surrounded  by  strap-shaped  ray  flowers, 
and  sometimes  (as  in  the  dandelion)  of 
strap-shaped  flowers  only. 
The  Compositce  are  ranked  as  the  highest  seed  plants.  They 
probably  owe  their  great  numbers  and  wide  distribution  over 
the  earth  largely  to  their  very  perfect  arrangements  for  securing 
pollination  and  fertilization.1  Part  of  their  success  is  no  doubt 
also  due  to  their  means  of  dispersing  seeds  by  the  wind,  as  in 
the  thistle,  dandelion,  and  other  genera  (Figs.  136  and  141)  ; 
or  by  animal  agency,  as  in  the  burdock,  Spanish  needle,  and 
the  cocklebur  (Figs.  135  and  352).  Compositce  are  very  fully 

1  See  Knuth-Davis,  Handbook  of  Flower  Pollination.  Clarendon  Press, 
Oxford. 


FIG.  302.  Flower  of  coffee 
and  a  fruit  partially  dis- 
sected to  show  the  seeds 

After  Karsten 


LEADING  FAMILIES  OF  FLOWERING  PLANTS     369 

represented  in  the  United  States,  and  some  genera,  such  as 
the  ironweed,  the  golden-rod  and  aster,  the  rosinweed,  the 
sunflower,  coreopsis,  and  Helenium,  are  either  exclusively 
American  or  at  any  rate  very  characteristic  of  our  flora.  The 
prairies  and  the  Great  Plains  especially  abound  in  composites. 


FIG.  303.  Flower  cluster  and  flowers  of  yarrow 

A,  flower  cluster ;  B,  section  of  flower  cluster ;  C,  a  ray  flower ;  D,  a  disk  flower. 

a,  anthers ;  ch,  chaff  of  disk ;  d,  disk  flowers ;  o,  ovary ;  re,  corollas  of  ray  flowers ; 

s,  stigmas ;  tc,  corolla  of  tubular  flower.   A,  B,  C,  seven  times  natural  size ;  D, 

eighteen  times  natural  size 

Food  plants  are  rather  rare  among  Compositce.  Lettuce  is 
the  most  generally  cultivated,  but  chicory  and  endive,  dande- 
lion, oyster  plant,  the  globe  artichoke,  and  the  Jerusalem  arti- 
choke are  of  some  value  as  food. 

Medicinal  Compositce  are  not  uncommon.  A  few  of  the  most 
familiar  are  arnica,  boneset,  camomile,  coltsfoot,  dandelion, 
tansy,  and  wormwood. 

Ornamental  plants  of  this  family  are  so  numerous  that  only 
a  small  proportion  of  them  can  here  be  mentioned.  Among 


370 


PEACTICAL  BOTANY 


these  are  bachelor's-button,  China  aster,  chrysanthemum  (in- 
cluding feverfew  and  marguerite),  coreopsis,  cosmos,  dahlia, 
English  daisy,  everlastings,  marigold,  sunflower,  zinnia. 

340.  Useful  plants  of  other  families.  Several  plants  belonging 
to  families  of  sympetalous  dicotyledons  not  already  described 
are  important  enough  to  be 
briefly  mentioned. 

The  Olive  family  (  Oleacece) 
furnishes  two  ornamental 
shrubs,  lilac  and  forsythia, 
and  an  important  genus  of 


D 

FIG.  304.  Akenes  with  various  types  of  pappus 

A,  Rudbeckia,  pappus  wanting ;  B,  Cichorium,  pappus  a  crown  of  fine  scales ;  (7, 
Coreopsis,  pappus  of  two  small  scales ;  D,  Helenium,  pappus  a  crown  of  conspicu- 
ous scales ;  E,  Cirsium,  pappus  a  tuft  of  plumose  hairs ;  F,  Lactuca,  pappus  borne 

on  a  long  beak 

timber  trees,  the  ash  genus.  The  olive  itself  is  probably  a 
native  of  the  eastern  Mediterranean  region.  It  is  now  con- 
siderably grown  in  California. 

The  G-ourd  family  (Cucurlitacece)  furnishes  many  edible 
fruits.  Of  these  the  pumpkin  and  the  summer  squashes  are  varie- 
ties of  the  same  species  and  the  large  winter  squashes  belong 
to  another  species  of  the  same  genus  (Cucurbita),  probably  of 
American  origin.  The  watermelon  belongs  to  a  genus  ( Citrul- 
lus)  of  Asiatic  origin.  The  muskmelons,  cantaloupes,  nutmeg 
melons,  and  the  cucumber  belong  to  a  third  genus  (  Cucumis) 
and  are  modified  forms  of  two  southern  Asiatic  species. 

The  Morning-glory  family  (Convolvulacece)  contains  one 
highly  useful  food  plant,  the  sweet  potato,  which  belongs  to 
the  same  genus  (Ipomoea)  with  some  of  the  morning-glories. 


CHAPTER  XXI 
FURTHER  DISCUSSION  OF  DEPENDENT  PLANTS 

341.  Nutrition,  the  leading  problem.   "Getting  a  living  is 
the  first  business  of  life,  and  food  is  the  basis  of  a  living ;  for 
the  body  derives  both  its  substance  and  its  energy  from  its 
food  "  (Needham).    This  statement  is  equally  true  of  plants 
and  of  animals,  and  the  greatest  problem  of  living  things  is 
how  they  are  to  obtain  an  adequate  supply  of  proper  food. 
Much  of  what  has  already  been  said  about  plants  has  to  do  in 
one  way  or  another  with  their  nutrition.  A  good  deal  has  also 
been  said  about  the  dependence  of  plants  upon  one  another 
and  upon  animals,  both  in  relation  to  food  and  to  reproduc- 
tion.   The  discussion  of  the  bacteria  and  other  fungi  (Chap- 
ters XI,  XIV,  and  XV),  though  it  deals  with  structures  and 
reproduction,  constantly  presents  the  relationships  of  these 
organisms  to  their  food  material.     There  are,  however,  some 
further  aspects  of  interdependence  which  we  shall  consider. 

342.  Kinds  of  dependence  for  nutrition.  Plants  such  as  forest 
trees,  ordinary  grasses,  cereals,  and  many  others  familiar  in  the 
farm  and  garden,  which  possess  chlorophyll,  can  manufacture 
their  own  food  (Chapter  II).    Since  these  green  plants  are 
dependent  for  materials  from  which  to  make  food  rather  than 
for  organized  food,  it  is  common  to  consider  them  as  inde- 
pendents.  This  does  not  mean  that  they  can  live  independent 
of  anything  outside  themselves,  but  that  if  carbon  dioxide, 
water,   certain  mineral  salts  containing  nitrogen,  potassium, 
etc.,  proper  light  and  temperature,  are  available  to  them,  they 
can  use  these  things  in  constructing  nourishing  foods.    These 
primary  foods  which  are. made  by  green  plants  are  directly  or 
indirectly  the  basis  of  the  foods  of  all  plants  which  are  not 
green,  and  of  all  the  food  of  animals,  which  in  this  wide  sense 

371 


372  JPBACTICAL  BOTANY 

are  dependents.  Usually  the  expression  dependent  organisms 
refers  to  an  intimate  life  association  between  two  or  more 
organisms.  All  such  life  associations  are  included  under  the 
term  symbiosis. 

A  good  illustration  of  the  different  kinds  of  symbiosis  is 
sometimes  seen  in  the  common  Indian-corn  plant  and  other 
plants  and  animals  that  live  upon  and  within  it.  Upon  the 
growing  cornstalk,  ear,  or  tassel,  the  dependent  corn  smut 
often  appears  (Fig.  197).  Most  of  this  fungus  grows  within 
the  tissues  of  the  living  corn  plant,  from  which  it  secures  its 
food.  This  particular  kind  of  symbiosis  is  known  as  parasit- 
ism, and  the  dependent  plant  is  known  as  a  parasite.  Later 
the  corn  plant  may  die  and  fall  upon  the  moist  ground,  when 
molds  and  bacteria  may  grow  upon  it.  These  take  their  nour- 
ishment from  the  dead  corn  plant,  and  as  they  do  so  they 
assist  in  bringing  about  its  decay.  Such  a  relation  is  known 
as  saprophytism,  and  the  plants  or  animals  which  live  upon 
dead  plants  or  animals  are  known  as  saprophytes. 

Still  another  phase  of  dependency  is  often  shown  by  small 
insects  known  as  aphids,  or  plant  lice,  one  kind  of  which 
thrives  upon  the  roots  of  corn.  Their  nourishment  consists  of 
the  juices  which  they  suck  from  the  tender  roots.  They  also 
excrete  a  sweetish  substance  called  honeydew,  which  is  used 
as  food  by  ants  and  sometimes  by  other  kinds  of  insects.  The 
aphids  may  begin  to  live  upon  corn  when  the  seedling  is  ger- 
minating, and  continue  upon  the  growing  plant  until  it  is 
mature.  Evidently  these  aphid  insects  are  parasites.  It  is  to 
be  further  noted  that  they  are  sluggish  insects,  and  although 
they  reproduce  rapidly  when  food  is  abundant,  they  are  not 
readily  able  to  pass  through  the  soil  or  over  its  surface  to  the 
roots  of  new  plants. 

There  is  a  common  black  field  ant  which  devours  the  honey- 
dew  apparently  with  great  relish.  Often  about  the  bases  of 
corn  plants  the  burrows  of  these  ants  may  be  seen.  They  dig 
tunnels  to  the  roots  of  the  corn,  then  carry  down  some  of  the 
aphids  and  place  them  upon  the  roots.  There  the  aphids 


DISCUSSION  OF  DEPENDENT  PLANTS          373 

are  cared  for  by  the  ants,  and  the  latter  secure  the  honeydew 
as  food.  Throughout  the  summer  and  autumn  the  ants  con- 
stantly care  for  the  aphids  and  their  young.  Aphid  eggs  are 
carried  to  places  most  favorable  for  their  hatching,  and  when 
the  young  are  hatched  they  are  transplanted  upon  tender 
young  roots.  When  disturbances  of  the  soil  threaten  destruc- 
tion to  the  eggs,  the  ants  seize  them  as  they  would  their 
own  eggs  and  carry  them  away.  At  the  beginning  of  the 
winter  aphid  eggs  are  carried  by  the  ants  into  the  deepest 
parts  of  the  ant  nests.  At  the  return  of  favorable  weather 
the  eggs  are  brought  forth  again  to  suitable  places  for  hatch- 
ing. In  this  case  the  aphids  which  are  parasitic  upon  the 
corn  roots  are  themselves  in  slavery  (Jielotism)  to  the  ants, 
and  this  interrelation  obviously  reaches  a  high  degree  of 
development. 

In  connection  with  the  corn  plant,  therefore,  we  have  an 
illustration  of  six  kinds  of  food  relations:  (1)  the  corn  is  a 
so-called  independent  plant,  since  it  is  able  to  manufacture 
carbohydrate  food  from  water  and  carbon  dioxide ;  (2)  men 
and  domesticated  animals  are  more  or  less  dependent  upon 
the  surplus  food  that  is  made  by  the  corn  plant  and  stored  in 
its  seeds  or  in  its  stalk ;  (3)  living  upon  corn  there  is  often 
found  the  plant  parasite  known  as  corn  smut ;  (4)  aphids  are 
placed  upon  corn  roots  by  ants,  the  aphids  being  parasites 
upon  the  corn ;  (5)  the  aphids  are  themselves  in  a  condition 
of  slavery  to  the  ants ;  (6)  after  death  the  corn  plant  may  be 
attacked  by  bacteria  and  molds,  which  as  saprophytes  assist 
in  bringing  about  its  decay. 

There  are  other  destructive  plants  and  animals  which  may 
attack  the  corn  plant,  but  these  will  not  now  be  discussed. 
Indeed,  almost  every  kind  of  plant  may  be  attacked  by  sev- 
eral kinds  of  dependent  organisms.  One  kind  of  dependency 
may  grade  into  another,  as  when  a  tree-destroying  fungus 
takes  its  food  from  a  living  tree,  and  after  the  tree's  death 
continues  to  live  upon  the  dead  body,  thus  changing  from 
parasitism  to  saprophytism. 


374  PRACTICAL  BOTANY 

343.  Dependent  relations  of  soil  bacteria.  Most  bacteria  are 
saprophytic.  Upon  and  within  the  soil  are  many  kinds  which 
get  their  nourishment  chiefly  from  the  organic  products  of 
plants  and  animals.  Saprophytic  bacteria,  as  they  grow  upon 
these  substances,  decompose  them  until  they  finally  no  longer 
appear  as  organic  materials  (Sect.  154,  Relation  of  bacteria 
to  decay).  Many  kinds  of  saprophytic  bacteria,  and  some  of 
the  parasitic  ones,  are  able  to  live  for  a  long  time  in  soils 
which  contain  only  a  very  small  amount  of  organic  matter. 
The  dependent  habit  of  these  saprophytic  forms  is  important, 
since  they  reduce  much  organic  matter  to  a  condition  in  which 
it  is  usable  in  the  growth  of  other  plants.  Conspicuous  among 
these  important  products  of  decay  are  the  nitrogen  compounds 
which  are  essential  to  growth  of  green  plants. 

There  are  four  groups  of  soil  bacteria  of  particular  interest 
in  this  connection.  First,  there  are  saprophytic  forms  which 
in  their  processes  of  nutrition  make  certain  compounds  of 
nitrogen  and  hydrogen  which  are  known  as  ammonia.  This 
bacterial  action  is  known  as  amnionification,  which  means  am- 
monia-making. The  bacteria  which  are  responsible  for  the 
action  are  called  the  "amnionification  bacteria."  Secondly, 
there  are  the  so-called  nitrite  bacteria,  which  in  their  processes 
of  nutrition  change  ammonia  into  compounds  in  which  there 
is  one  part  of  nitrogen  to  each  two  of  oxygen.  Such  com- 
pounds are  known  as  nitrites.  Thirdly,  there  are  the  nitrate 
bacteria,  which  change  nitrites  into  compounds  in  which  there 
is  one  part  of  nitrogen  to  each  three  of  oxygen.  Such  com- 
pounds are  known  as  nitrates.  These  last  two  processes  are 
spoken  of  as  nitrification.  And  fourthly,  there  are  still  differ- 
ent bacteria  (Sect.  37,  Chapter  III)  which  at  times  enter  the 
roots  of  certain  kinds  of  plants,  as  clover,  soy  beans,  peas,  and 
alfalfa.  When  some  of  these  bacteria  have  entered  the  roots 
they  are  surrounded  by  tissue  so  as  to  form  nodules  or  tuber- 
cles (Fig.  305).  Within  these  tubercles  the  bacteria  are  able 
to  take  uncombined  nitrogen  from  the  air  and  to  combine 
it  with  oxygen  in  such  a  way  as  to  form  nitrates.  These 


DISCUSSION  OF  DEPENDENT  PLANTS 


375 


tubercle  bacteria  are  known  as  the  nitrogen-fixing  bacteria, 
since  they  fix  free  nitrogen  from  the  air.  Since  the  ordinary 
grain-producing  plants  of  the  fields  must  have  nitrogen  in 
order  to  grow,  and  since  they  can  use  it  only  in  the  nitrate 
form,  the  significance  to  agricultural  plants  of  the  work  of 
these  root-tubercle  or  nitrogen-fixing  bacteria  is  evident.  An 
experiment  may 
readily  be  per- 
formed (Fig.  306) 
to  determine  the 
relative  influence 
of  these  organisms 
upon  the  rate  and 
amount  of  plant 
growth.  At  the 
death  of  the  clo- 
vers, peas,  beans, 
etc.,  upon  which 
the  tubercles  have 
grown,  those  sur- 
plus nitrates  left 
in  the  soil  furnish 
a  most  important 
part  of  the  food 
of  other  agricul- 
tural plants. 

We  have,  there- 
fore, at  least  four 
kinds  of  depend- 
ent soil  bacteria,  each  of  which  in  its  processes  of  nutrition 
transforms  nitrogen  compounds  in  such  a  way  that  those  com- 
pounds are  eventually  available  as  food  for  higher  plants.  The 
importance  of  this  is  further  indicated  in  Sect.  37  (Partnership 
of  roots  and  bacteria)  and  in  Chapter  XXIV.  There  are  yet 
other  kinds  of  bacteria  which  break  up  organic  compounds  so 
as  to  release  nitrogen  into  the  air,  the  process  being  known  as 


FIG. 305.  Roots  of  red  clover,  with  tubercles  in  which 
are  the  bacteria  that  collect  nitrogen  from  the  air 

One  half  natural  size 


FIG.  306.  Cultures  of  peas  of  same  age  and  same  kind  of  seed,  one  with  and 

one  without  root-tubercle  bacteria.  After  Frank 

376 


DISCUSSION  OF  DEPENDENT  PLANTS          377 

denitrification.  In  discussing  the  dependent  relations  of  these 
bacteria  we  may  mention  another  dependent  organism  which 
has  recently  been  described.1  In  the  soil  a  very  small  animal, 
closely  resembling  the  amoeba,  is  said  to  devour  the  bacteria 
of  nitrification.  This,  if  true,  adds  a  new  feature  to  what 
we  have  known  of  the  interdependency  of  life  in  the  soil.  If 
these  amoeba-like  animals  become  very  abundant,  they  may 
destroy  so  many  of  the  nitrifying  bacteria  that  comparatively 
little  nitrification  will  occur.  Hence  a  smaller  amount  of 
nitrites  and  nitrates  will  be  produced,  and  hence  less  nitrogen 
food  from  this  source  will  be  available  for  higher  plants.  But 
it  is  asserted  that  there  tends  to  be  a  "balance  of  life,"  since, 
if  the  nitrifying  bacteria  of  any  locality  are  nearly  exhausted, 
the  food  supply  of  the  animal  that  lives  upon  them  is  thereby 
so  reduced  that  for  a  time  it  does  not  thrive  so  well.  Mean- 
time the  accumulating  compounds  offer  greater  food  supply 
to  nitrifying  bacteria,  and  then  for  a  time  they  may  flourish, 
until  when  again  they  are  abundant  they  offer  increased  food 
for  the  organisms  that  prey  upon  them.  In  this  way  a  very  long 
predominance  of  any  kind  of  organism  is  usually  prevented 
by  the  fact  that  its  abundance  offers  new  opportunities  for 
the  development  of  organisms  that  can  use  it  as  food. 

A  significant  artificial  method  of  regulating  the  growth  of 
this  amoeba-like  organism  was  almost  accidentally  discovered. 
Upon  the  roots  of  the  grapevine  there  sometimes  lives  an  in- 
sect parasite  known  as  phylloxera.  It  was  found  in  France 
that  a  treatment  of  the  soil  in  the  vineyards  with  carbon  disul- 
phide,  though  an  expensive  process,  would  prevent  the  growth 
of  phylloxera.  The  fact  that  after  such  treatment  the  soil  con- 
tained more  nitrates  and  nitrites  than  before  led  investigators 
at  Harpenden,  England,  to  studies  from  which  they  state  that 
the  carbon  disulphide  not  only  kills  phylloxera,  but  also  kills 
most  or  all  of  the  amoeba-like  animals  which  live  upon  nitri- 
fying bacteria.  It  does  not  seriously  interfere  with  the  activi- 
ties of  the  bacteria  that  break  up  the  ammonia  compounds, 
i  Hall,  A.  D.,  Science,  Vol.  XXXII,  pp.  363-371,  1910. 


378  PRACTICAL  BOTANY 

Therefore  treatment  with  carbon  disulphide  is .  said  not  only 
to  prevent  phylloxera  from  living  upon  the  roots  of  the  grape, 
but,  by  killing  the  amoeba-like  animals,  to  make  it  possible  for 
the  bacteria  of  nitrification  to  produce  more  ammonia  com- 
pounds within  the  soil  than  would  be  produced  if  the  bac- 
teria were  themselves  being  preyed  upon  by  their  enemies. 

The  student  must  clearly  understand  that  there  are  many 
kinds  of  soil  bacteria.  The  above  statement  includes  a  few 
facts  from  a  very  intricate  and  as  yet  incompletely  under- 
stood subject. 

344.  Dependent  relations  of  parasitic  bacteria.  In  addition 
to  what  was  said  in  the  chapter  on  bacteria,  but  a  brief  state- 
ment need  here  be  made  regarding  the  dependent  habit  of 
parasitic  bacteria.  Many  kinds  of  bacteria  may  take  their  food 
directly  from  other  living  things,  and  are  wholly  or  partially 
dependent  upon  living  hosts  for  their  food. 

The  bacteria  which  cause  "  pear  blight "  may  be  taken  as 
an  illustration  of  the  nature  and  degree  of  dependence  that 
may  exist.  This  is  a  disease  which  often  seriously  affects  the 
leaves,  young  twigs,  and  fruit  of  the  pear  and  apple.  The 
bacteria  cannot  live  under  long  exposure  to  direct  sunlight  or 
to  drying,  but  can  endure  low  temperatures.  During  the  winter 
they  live  in  the  diseased  twigs.  In  the  early  growing  season 
the  leaves  and  young  growth  of  the  twigs  become  blackened 
and  soon  wilt  as  a  result  of  the  internal  growth  of  the  parasite. 
The  bacteria  secure  nourishment  from  the  cells  of  the  host. 
They  may  act  so  as  partially  or  wholly  to  stop  the  cellular 
passages  of  the  host,  and  possibly  are  injurious  in  other  ways. 

The  question  of  how  these  bacteria  are  distributed  to  new 
hosts  is  important.  Even  if  they  should  be  carried  through  the 
air,  and  should  withstand  the  consequent  drying  and  sunshine, 
and  fall  upon  the  surfaces  of  twigs,  leaves,  or  fruit  of  the 
proper  host,  it  is  said  that  they  could  not  make  their  way  into 
the  tissue.  It  is  believed  that  the  common  means  of  infection 
is  through  biting  or  stinging  insects,  or  nectar-hunting  insects 
that  visit  the  flowers  and  fruit.  When  a  few  bacteria  are 


DISCUSSION  OF  DEPENDENT  PLANTS          379 

inserted  into  a  new  twig,  leaf,  or  floral  structure,  the  infec- 
tion may  spread  several  inches  and  soon  the  blighting  begins. 
When  one  flower  is  infected,  insects  may  carry  the  bacteria 
to  practically  every  flower  upon  the  tree  or  upon  other  trees 
within  the  vicinity.  Moreover,  when  the  disease  has  developed 
far  enough  for  the  characteristic  gummy  exudations  to  appear, 
insects  that  bite  into  them  may  become  loaded  with  the  bac- 
teria and  may  insert  some  of  them  into  a  new  host.  In  prun- 
ing both  diseased  and  healthy  twigs,  the  knife  may  be  the 
means  of  transferring  bacteria.  If  all  infected  parts  are  re- 
moved and  burned,  and  if  the  knife  used  in  pruning  diseased 
twigs  is  sterilized  before  being  used  in  pruning  healthy  plants, 
the  continued  spread  of  the  disease  is  made  unlikely. 

The  "  pear-blight "  bacteria,  therefore,  are  dependent  upon 
such  plants  as  the  apple  and  pear  for  nutrition,  dependent  upon 
their  twigs  for  protection  through  the  winter,  and  dependent 
chiefly  upon  insects  for  distribution  to  new  hosts.  This  is 
but  one  of  many  illustrations  that  might  be  cited  to  show  the 
degree  of  dependence  to  which  parasitic  bacteria  have  come. 

345.  Other  saprophytic  fungi.  One  has  but  to  observe  care- 
fully in  any  deeply  shaded,  moist,  and  warm  undergrowth  to 
see  abundant  illustrations  of  molds,  mushrooms,  and  toadstools 
which  are  dependent  upon  decaying  organic  matter.  Usually 
the  major  portion  of  such  a  saprophytic  plant  lives  within  the 
supporting  substance  and  gathers  nourishment  from  it.  In 
this  way  the  saprophyte  may  live  for  months  or  years  with  no 
external  appearance  of  its  growth.  Upon  breaking  open  an  old 
log  or  stump,  or  upturning  the  soil,  one  often  finds  the  exten- 
sively interwoven  network  of  a  saprophytic  fungus.  After  a 
period  of  growth  by  the  mycelium  of  the  saprophyte,  its  super- 
ficial reproductive  structure  develops  under  favorable  condi- 
tions as  a  sort  of  final  and  outward  expression  of  its  previous 
more  or  less  prolonged  period  of  nutrition.  Spores  thus  pro- 
duced may  be  carried  by  agencies  such  as  the  wind,  insects,  or 
other  animals.  When  they  fall  in  favorable  locations  they  ger- 
minate, penetrate  nutrient  substances,  and  continue  the  life 


380  PEACTICAL  BOTANY 

round.  In  the  chapters  on  fungi  there  were  given  detailed 
accounts  of  the  processes  and  structures  that  have  to  do  with 
the  nutrition  of  several  kinds  of  saprophytic  as  well  as  para- 
sitic fungi. 

346.  Other  parasitic  fungi.    Usually  parasitic  fungi  are  ex- 
tremely dependent,  since  most  of  them  can  live  on  but  one  or 
at  most  a  few  kinds  of  hosts.    If  for  any  reason  these  hosts  are 
lacking,  or  if  the  parasite  is  not  properly  placed  upon  or  within 
the  host,  the  parasite  fails.    Wheat  and  oat  rust  may  thrive 
upon  wheat  and  oats  and  produce  their  summer  and  winter 
spores  in  great  quantities  (Sect.  232).    But  in  entire  absence 
of  wheat  and  oats  the  parasite  would  probably  soon  disappear. 
It  is  apparently  well  adjusted  to  life  upon  these  hosts,  but, 
correspondingly,  thoroughly  dependent  upon  them  for  nour- 
ishment.   Such  is  the  case  with  many  parasitic  fungi.    Their 
close  adjustment  to  life  upon  one  type  of  host  is  accompanied 
by  complete  dependence  upon  that  host.    It  may  be  easier  for 
the  dependent  plant  to  secure  food  when  it  is  well  located,  but 
it  encounters  serious  dangers  when  not  well  located. 

347.  Degrees  of  dependence  among  flowering  plants.    Some 
dependent  flowering  plants,  like  the  woodbine  or  Virginia 
creeper,  are  almost  independent.    A  woodbine  may  grow  in  the 
open  and  attain  its  full  size  ;  but  in  dense  woodlands  woodbines, 
grapevines,  and  many  other  climbers  can  only  make  a  normal 
growth  by  raising  themselves  into  the  light  by  climbing  up 
the  trunks  of  trees.    Similar  degrees  of  dependence  are  found 
among  the  members  of  most  of  the  other  groups  of  plants 
described  in  the  succeeding  sections  of  this  chapter. 

348.  Kinds  of  dependent  flowering  plants.    The  principal 
groups  into  which  dependent  flowering  plants  are  divided 
are  as  follows: 

(1)  Lianas,  or  climbers. 

(2)  Epiphytes,  or  plants  which  live  perched  upon  other 
plants. 

(3)  Saprophytes,  or  plants  which  live  on  the  products  of 
the  decay  of  organic  matter. 


DISCUSSION  OK  DEPENDENT  PLANTS         381 

(4)  Parasites,    or    plants   which   live   upon    other   plants 
(known  as  host  plants)  while  the  latter  are  still  alive.1 

(5)  Carnivorous  plants,  or  those  which  capture  small  ani- 
mals (such  as  insects)  and  live  at  least  in  part  upon  them. 

Types  of  lianas  were  mentioned  in  the  preceding  section. 
They  can  get  their  living  without  the  aid  of  other  plants.  The 
other  groups  (2~5)  are  discussed  in  the  following  sections.2 

349.  Epiphytes.  Unfortunately  for  the  student  in  temperate 
climates,  flowering  epiphytes  are  mainly  confined  to  the  tropics. 


FIG.  307.   Indian  pipe  (Monotropa  uniflora),  a  symbiotic  saprophyte 
The  plants  are  white  from  lack  of  chlorophyll 

The  Spanish  moss  (Figs.  367  and  368)  is  one  of  the  few  excep- 
tions. A  visit  to  any  large  greenhouse  in  which  orchids  are 
kept  will,  however,  suffice  to  give  a  fair  idea  of  the  appearance 
of  some  of  the  most  characteristic  plants  which  live  perched 
upon  the  trunks  or  branches  of  trees.  Since  these  plants  usu- 
ally have  little  or  no  permanent  water  supply  about  their  roots, 
they  must  be  provided  with  means  of  absorbing  water  rapidly 
during  rains,  and  for  resisting  drying  between  one  rainfall  and 
the  next.  The  Spanish  moss  (which  is  rootless)  takes  up  water 

1  Cases  of  parasitism  of  plants  upon  living  animals,  although  only  too 
common  among  the  lower  plants  (Sects.  157-160),  are  unknown  among  the 
higher  ones. 

2  See  Warming,  (Ecology  of  Plants,  chap.  xxv. 


382 


PRACTICAL  BOTANY 


along  the  surface  of  the  stems  by  the 
aid  of  special  absorbent  hairs  which 
grow  from  the  epidermis.  This  plant 
can  become  almost  dried  up  without 
permanent  injury.  Orchids  like  Cattleya 
(Fig.  20)  frequently  have  long,  dan- 
gling roots,  covered  with  an  absorb- 
ent layer  of  tissue  which  acts  much  like 
blotting  paper,  taking  up  water  very 
promptly,  and  gradually  releasing  it  for 
the  use  of  the  plant.  Many  epiphytes  of 
this  type  have  thickened,  fleshy  stems, 
or  leaves,  or  both,  and  a  thick  epidermis, 
through  which  little  water  escapes. 

350.  Saprophytes.  In  general,  the 
seed  plants  which  are  saprophytes  occur 
only  in  the  forest  or  under  shrubs.  It  is 
in  such  situations  that  plants  find  a  most 
abundant  supply  of  humus,  or  decaying 
organic  matter.  Complete  saprophytes  — 
that  is,  those  which  cannot  exist  without 
an  abundant  supply  of  soluble  organic 
matter  in  the  soil  or  substratum  —  are 
always  pale,  or  even  white,  from  partial 
or  complete  absence  of  chlorophyll  (Figs. 
307,  308).  Their  leaves  are  small  and 
scale-like.  Their  roots  are  usually  short, 
little  branched,  and  furnished  with  a 
mycorrhiza,  which  freely  absorbs  plant 
food  from  the  substratum. 

Partial  saprophytes,  among  flowering 
plants,  are  not  easily  recognized  by 
their  form  and  color,  but  may  be  known 
by  their  inability  to  flourish  without  FIG.  308.  Pinesap  (Mono- 
considerable  humus  in  the  soil.  Theirre-  ^SSSSS^SS^ 
quirements  in  this  respect  differ  greatly,  dependent  on  mycorrhiza 


DISCUSSION  OF  DEPENDENT  PLANTS         383 

351.  Parasites.  The  dodders  are  the  most  familiar  flowering 
parasites.  One  of  the  commonest  species  is  abundant  in  the 
central  and  northeastern  states,  its  thread-like,  golden-yellow 
stems  forming  great  tangled  masses  on  many  kinds  of  plants, 
from  goldenrods  to  willows,  growing  in  damp  places.  The 
dodders  and  some  root  parasites,  such  as  the  beechdrops, 
squawroot,  and  cancer-root  (  Orobanche,  Fig.  309),  are  complete 


FIG.  309.  Two  plants  of  cancer-root  (Orobanche)  at  left  and  middle  of  figure, 
parasitic  on  the  roots  of  a  wormwood  at  the  right 

parasites,  and  have  no  green  foliage.  Other  plants,  such  as  the 
mistletoe,  have  green  leaves  and  do  photosynthetic  work,  but 
depend  on  the  host  for  water  and  the  mineral  substances  dis- 
solved in  it.  Such  plants  are  called  partial  parasites. 

352.  Development  of  parasite  seedlings.  The  embryo  of  the 
dodder  is  a  thread-like  object,  which  lies  coiled  in  a  spiral  in 
the  endosperm  of  the  seed.  The  seed  germinates  late  in  the 
spring,  and  the  seedling  at  first  appears  as  a  very  slender, 
naked  stem,  with  a  club-shaped  lower  extremity  which  is  soon 


384 


PRACTICAL  BOTANY 


pushed  underground.  The  upper  portion  of  the  stem,  if  it  en- 
counters a  twig  or  small  plant,  quickly  winds  about  it  and 
sends  sucking  roots  or  haustoria  into  the  tissues  of  the  host. 
By  means  of  these  it  draws  from  the  host  enough  plant  food 
to  develop  the  dodder  plant  until  it  flowers  and  seeds.  If  it 
encounters  no  suitable  host  plant  in  the 
course  of  four  or  five  weeks,  the  seed- 
ling dies. 

Some  extraordinary  flowering  para- 
sites develop  scarcely  any  stem,  but  con- 
sist mainly  of  haustoria  and  an  immense 
flower.  Rafflesia,  the  most  remarkable 
of  these,  grows  upon  the  roots  of  vines 
which  run  along  the  surface  of  the 
ground.  The  buds  of  the  largest  species 
of  Rafflesia  on  emerging  from  the  bark 
of  the  host  are  about  as  large  as  walnuts. 
They  finally  increase  in  size  until  they 
become  very  large  and  cabbage-like,  after 
which  each  bud  opens  into  a  fleshy,  ill- 
smelling  flower  forty  inches  in  diameter, 
closely  attached  by  its  haustoria  to  the 
root  of  the  host,  which  looks  as  if  it  bore 
flowers  of  its  own. 
353.  Damage  inflicted  by  parasites.  So  much  water  and 
plant  food  is  taken  from  the  host  by  many  parasites  that  they 
may  cause  serious  injury  to  cultivated  plants  and  to  forest 
trees.  The  flax  dodder  and  the  clover  dodder  often  do  great 
damage  to  crops  in  this  country  and  in  Europe,  and  another 
species1  is  sometimes  troublesome  in  fields  of  alfalfa.  The 
American  mistletoe  is  so  injurious  to  dicotyledonous  trees  in 
the  Southwestern  States  that  it  often  has  to  be  cut  off  from 
the  trees  to  enable  them  to  thrive.  The  European  mistletoe 
causes  much  damage  to  apple  trees  in  northern  France  and 
in  the  Tyrol. 

1  Ouscuta  arvensis. 


FIG.  310.  A  piece  of  fir 

wood  penetrated  by  the 

roots  of  the  European 

mistletoe 

After  Kerner 


DISCUSSION  OF  DEPENDENT  PLANTS 


385 


354.    Carnivorous  plants.  There  are  many  kinds  of  plants 1 
which  capture  insects  and  other  small  animals.    In  some  cases, 

at  least,  they  may  use  the 
captured  animals  as  a  part  of 
then?  food  supply.  These  plants 
may  be  roughly  classified  into 
(1)  plants  which  capture  their 
prey  by  means  of  sticky  secre- 
tions; (2)  plants  which  capture 
their  prey  by  means  of  hollow, 
trap-like,  motionless  leaves ; 
(3)  plants  which  capture  their 
prey  by  means  of  moderately 
quick  movements  of  a  sensitive 
hinged  leaf. 

It  would  take  too  much  space 
to  discuss  these  classes  of  car- 
nivorous plants  in  detail,  so  a 
brief  account  of  one  representa- 
tive of  each  class  must  suffice. 
355.  The  sun- 
dews.    These 
are  low  marsh 
plants,    having 
hairy  leaves  and 
slender  flower 
stalks  on  which 
are  borne  small 
white    flowers 
(Fig.  311).    In 
one  of  the  com- 
monest species 


the   leaf    con- 


FIG. 311.  Sundew  (Drosera  rotundifolia) 

sists  of  a  roundish  blade  borne  on  a  moderately  long  leaf- 
stalk. On  the  inner  surface  and  round  the  margin  of  the  blade 
i  Probably  more  than  four  hundred  species. 


386 


PRACTICAL  BOTANY 


FIG.  312.    Blade  of  leaf 
of  sundew  without  prey 

Somewhat  magnified 


(Fig.  312)  are  borne  a  number  of  short  bristles,  each  termi- 
nating in  a  knob  which  is  covered  with  a  clear,  sticky  liquid. 
When  a  small  insect  touches  one  of  the 
sticky  knobs  it  may  be  held  fast,  and  in 
that  case  the  hairs  at  once  begin  to  close 
over  it,  as  shown  in  Fig.  313.  The  insect 
soon  dies  and  then  usually  remains  for 
many  days,  while  the  leaf  pours  out  a 
juice  by  which  the  soluble  parts  of  the  in- 
sect are  digested.  The  liquid  containing 
the  digested  portions  is  absorbed  by  the 
leaf,  and  contributes  an  important  part 
of  the  nourishment  of  the  plant,  while 
the  undigested  fragments,  such  as  legs 
and  wing  cases,  remain  on  the  surface 
of  the  leaf  or  may  drop  off  after  the  hairs 
let  go  their  hold  on  the  captive  insect. 
356.  Pitcher  plants.  In  the  ordinary  pitcher  plants  (Fig.  314) 
the  leaf  appears  in  the  shape  of  a  more  or  less  hooded  pitcher. 
These  pitchers  are  usu- 
ally partly  filled  with 
water,  and  in  this  water 
many  drowned  and  de- 
caying insects  are  com- 
monly to  be  found.  The 
insects  have  flown  or 
crawled  into  the  pitcher, 
and,  once  inside,  have 
been  unable  to  escape 
on  account  of  the  dense 
growth  of  bristly  hairs 
about  the  mouth,  all 
pointing  inward  and 
downward.  The  com- 
mon, American  pitcher  plants  may  not  depend  much  on  ani- 
mal food,  but  it  is  certain  that  some  tropical  species  require  it. 


FIG.  313.  Leaves  of  sundew  during  diges- 
tion of  captured  prey 

The  one  at  the  left  has  all  its  tentacles  closed ; 

the  one  at  the  right  has  half  of  them  closed 

over  captured  prey.   Somewhat  magnified 


DISCUSSION  OF  DEPENDENT  PLANTS 


387 


357.  The  Venus's-flytrap.     In  the  Venus  Vflytrap,  which 
grows  in  the  sandy  regions  of  eastern  North  Carolina,  the  mech- 
anism for  catching  insects  is  still  more  remarkable.    The  leaves, 
as  shown  in  Fig.  315,  terminate  in  a  hinged  portion  which  is 
surrounded  by  a  fringe  of 

stiff  bristles.  On  the  in- 
side of  each  half  of  the 
trap  grow  three  short  hairs. 
The  trap  is  so  sensitive 
that  when  these  hairs  are 
touched  it  closes  rather 
rapidly,  and  very  generally 
succeeds  in  capturing  the 
fly  or  other  insect  which 
has  sprung  it.  The  im- 
prisoned insect  then  dies 
and  is  digested,  —  some- 
what as  in  the  case  of  those 
caught  by  the  sundew,  — 
after  which  the  trap  re- 
opens, and  is  ready  for 
fresh  captures. 

358.  Advantages  of  ani- 
mal   food.     It    has    been 
claimed  that  there  is   an 
advantage  that  comes  to  a 
good  many  kinds  of  plants 
which  catch  insects  and  ab- 
sorb the  digested  products. 
Carnivorous  plants  belong 

usually  to  one  of  two  classes  as  regards  their  place  of  growth ; 
they  are  bog  plants  or  air  plants.  In  either  case  their  roots 
find  it  difficult  to  secure  much  nitrogen-containing  food, — 
that  is,  much  food  out  of  which  protein  material  can  be  built  up. 
Animal  food,  being  itself  largely  protein,  is  admirably  adapted 
to  nourish  the  growing  parts  of  plants,  and  those  which  have 


FIG.  314.     Common  pitcher  plant 
(Sarracenia  purpurea) 

At  the  right  one  of  the  pitcher-like  leaves 
is  shown  in  cross  section 


388 


PRACTICAL  BOTANY 


insect-catching  powers  stand  a  far  better  chance  to  exist  as 
air  plants,  or  in  the  thin,  watery  soil  of  bogs  than  ordinary 
plants  which  have  no  such  habits. 

359.  Irritability  in  plants.1  The  popular  notion  of  what 
plants  can  do  does  not  credit  them  with  any  power  to  execute 
movements.  It  is  true  most  people  have  heard  of  sensitive 
plants,  which  fold  up  their  leaflets  when  touched.  Every  one 

who  is  very  observant  must 
have  noticed  such  move- 
ments as  those  of  bean, 
clover,  and  other  leaves  in 
taking  the  nocturnal  posi 
tion  (Figs.  52-54). 

Even  people  who  are  not 
botanists  are  usually  much 
impressed  when  they  see  for 
the  first  time  such  prompt 
and  apparently  purposeful 
movements  as  those  by 
which  the  stamens  of  the 
barberry  flower  spring  up 
upon  being  touched,  or 
those  by  which  the  Venus's- 
flytrap  catches  insects.  But 
in  general  the  movements 
of  plants  are  executed  so 
slowly  that  the  change  of 
position  of  the  plant  as  a  whole,  or  of  its  parts,  can  only  be 
discerned  by  magnifying  the  motion  in  some  way  or  by  noting 
the  successive  positions  occupied  at  considerable  intervals  of 
time.  And  yet  plants  do  move  so  generally  that  in  comparing 
them  with  animals  we  can  only  say  that  "  most  animals  are 
more  active  than  most  plants." 

All  of  the  actions  of  plants  are  due  to  the  irritability  of 
their  protoplasts.    By  this  is  meant  simply  their  power  of 
1  See  Coulter,  Barnes,  and  Cowles,  Textbook  of  Botany,  Vol.  I,  chap.  v. 


FIG.  315.  VenusVflytrap 


DISCUSSION  OF  DEPENDENT  PLANTS         389 

responding  in  any  way  to  some  application  of  energy  which 
serves  as  a  stimulus.  Professor  W.  Pfeffer  thus  illustrates  the 
chain  of  events  that  occurs :  An  alarm  clock  which  is  wound 
up,  but  not  going,  receives  a  shake  (stimulus)  which  starts  its 
wheels,  so  that  after  a  time  (latent  period)  the  clock  sounds 
its  alarm  (result).  The  sensitiveness  of  the  clock  to  the  jar 
which  starts  it,  corresponds  to  the  irritability  of  the  proto- 
plasm. Among  the  stimuli  which  call  forth  responses  from 
protoplasm  are  heat,  light,  electricity,  gravity,  pressure  of 
external  objects,  and  contact  with  substances  which  produce 
chemical  effects  on  the  protoplasm. 

360.  Examples  of  responses  to  stimulation.  The  earlier 
chapters  of  this  book  are  full  of  instances  of  irritability  called 
into  action  by  appropriate  stimuli.  Indeed,  the  whole  life  his- 
tory of  a  plant  is  a  series  of  responses  to  stimuli ;  every  newly 
sown  wheat  field  in  which  the  grain  lies  comparatively  in- 
active during  a  succession  of  cold  days,  and  then,  when 
warmer  weather  comes,  suddenly  begins  to  sprout,  is  an  ex- 
cellent illustration  of  the  response  of  protoplasm  in  the  seed 
to  heat. 

Responses  to  light  are  very  common,  one  of  the  most  evi- 
dent being  the  prompt  excretion  of  oxygen  noted  when  a 
green  aquatic  plant  arranged  as  shown  in  Fig.  12  is  brought 
from  darkness  into  sunlight. 

The  response  to  gravity  is  shown  by  the  downward  growth 
of  the  roots  and  upward  growth  of  the  stem  in  very  young 
seedlings. 

The  response  to  pressure  is  most  evident  in  the  coiling  of 
a  tendril  about  any  slender  support,  which  begins  almost  as 
soon  as  the  tendril  touches  the  foreign  object. 

Responses  to  chemical  stimuli  are  extremely  common  and 
of  great  importance  in  the  life  of  the  plant.  One  familiar 
instance  is  the  manner  in  which  roots  grow  toward  masses  of 
fertilizer  or  rich  soil  (Fig.  348).  Another  case  is  the  huddling 
of  swarms  of  bacteria  about  a  filament  of  any  green  alga 
which  is  giving  off  oxygen  during  photosynthesis. 


CHAPTER  XXII 


TIMBER:  FORESTRY 

361 .  Coniferous  woods.  Our  native  woods 1  are  best  classified 
into  the  two  principal  groups  of  soft  (or  coniferous)  and  hard 
woods.2  The  needle-leaved  or  coniferous  trees  of  the  country  fur- 
nish more  than  three  quar- 
ters of  our  timber  supply. 
The  structure  of  conif- 
erous wood,  as  seen  for  ex- 
ample on  the  end  of  a  beam 
cut  off  squarely,  or  on  a 
new  lead  pencil,  is  in  one 
respect  less  complex  than 
that  of  most  hard  woods  : 
the  wood  is  chiefly  com- 
posed of  tracheids,  long 
tubular  cells  with  taper- 
ing ends,  and  contains  no 
continuous  ducts  (it  may 
contain  resin  passages). 
The  rings  plainly  seen  on 
the  cross  section  of  some 
kinds  are  due  to  the  dif- 
ference in  diameter  of  the 


a.r 


a.r 


FIG.  316.   Cross  section  of  typical  conif- 
erous wood  of  white  pine 


a.r,  boundaries  between  one  year's  growth, 
or  "annual  ring,"  and  the  next;  the  large, 
roundish  white  spots  are  cut-off  resin  pas- 
Magnified  fifteen  diameters.  Photo- 
micrograph by  R.  B.  Hough8 


tracheids  formed  in  early 
spring  and  later  (Fig.  316). 

1  "Timber,"  Bulletin  10,  Division  of  Forestry,  U.S.  Dept.  Agr.,  1895. 

2  Some  of  the  needle-leaved  or  coniferous  trees,  such  as  the  larch  and  the 
yew,  have  rather  hard  wood;  and  some  broad-leaved  trees,  such  as  willows, 
poplars,  tulip  trees,  and  buckeyes,  have  soft  wood;  but  people  who  deal  in 
timber  usually  speak  of  the  two  general  classes  as  explained  above. 

8  From  Handbook  of  the  Trees  of  the  Northern  States  and  Canada,  writ- 
ten and  published  by  Romeyn  B.  Hough,  Lowville,  New  York. 

390 


TIMBEE:  FORESTRY 


391 


a.r 


362.  Hard  woods.  North  America  furnishes  more  species  of 
trees  valuable  for  hard-wood  timber  than  any  other  region 
of  similar  area  with  a  temperate  climate.  About  eighty  kinds 
are  of  economic  importance,  and  of  these,  six  or  eight  are  oaks, 
classed  for  commercial  purposes  as  white  and  red  or  black 
oaks.  White  oak  is  stronger  than  the  red  kinds,  but  has  not 
so  coarse  a  grain,  so  that 
for  cabinetmaking  the  red 
oaks  are  more  ornamental, 
and  often  in  "quartered" 
cut  lumber  (sawed  radially) 
are  very  showy.  More  than 
half  of  our  supply  of  hard- 
wood timber  is  furnished 
by  the  oaks  (of  about  nine- 
teen species). 

Among  the  woods  of 
broad-leaved  trees,  tulip- 
wood,  from  the  tulip  tree 
(Liriodendrori),  is  next  in 
importance  to  the  various 
kinds  of  oak.  It  is  variously 
known  as  yellow  poplar, 
and  whitewood,  and  grows 
in  abundance  in  the  Ohio 
basin  and  southward,  but 
does  not,  like  oak,  form 
separate  forests.  The  wood 
is  very  soft  and  workable,  and  has  largely  taken  the  place  of 
white  pine  for  the  inside  finish  of  houses  and  in  the  manu- 
facture of  woodenware. 

Ash,  beech,  birch,  chestnut,  elm,  maple,  red  gum,  and  syca- 
more are  some  of  the  most  important  hard  woods  for  general 
purposes  besides  those  already  mentioned.  For  especial  pur- 
poses certain  woods  not  of  the  greatest  value  for  all-round 
construction  are  highly  prized ;  as  hickory  for  ax  and  other 


a.r 


FIG.  317.    Cross  section  of  ring-porous 
wood  of  sassafras 

a.r,  boundaries  of  the  "  annual  rings" ;  the 
wood  is  ring-porous  because  the  ducts  (here 
shown  as  oval  or  roundish  spots)  are  most 
abundant  in  the  spring  wood,  almost  lack- 
ing in  autumn  wood.  Magnified  fifteen  di- 
ameters. .  Photomicrograph  by  R.  B.  Hough 


392 


PRACTICAL  BOTANY 


tool  handles,  and  for  carriage  spokes;  beech  for  shoemakers' 
lasts,  saw  handles,  and  carpenters'  planes;  persimmon  for 
wood  turning  and  shoe  lasts ;  black  locust  for  posts  and  rail- 
road ties  (on  account  of  its  durability  in  the  ground). 

For  cabinetwork  the  most  valued  of  our  hard  woods  are 
black  walnut,  cherry,  birch,  and  a  good  many  species  of  oak 
and  of  ash.  White  walnut,  red  or  sweet  gum  (Liquidambar), 
sycamore,  and  holly  are  also  used,  although  not  so  largely. 


B 
FIG.  318.  Cross  section  of  diffuse-porous  woods     . 

A,  coarse-grained  wood  of  sycamore ;  B,  fine-grained  wood  of  holly.  The  wood  is 
diffuse-porous  because  the  ducts  are  formed  somewhat  equally  throughout  the 
season's  growth ;  the  dark  streaks  running  nearly  vertically  on  the  page,  as  the 
sections  are  here  placed,  are  medullary  rays  (shown  more  clearly  in  Fig.  35).  Mag- 
nified fifteen  diameters.  Photomicrograph  by  R.  B.  Hough 

In  structure  the  broad-leaved  woods  may  be  classed  into 
two  groups,  —  the  ring-porous  and  the  diffuse-porous  kinds.  In 
the  former  group  (Fig.  317)  most  of  the  conspicuous  ducts 
(the  cut-off  ends  of  which  appear  as  pores  in  the  cross  section) 
are  found  in  the  spring  wood.  In  the  latter  the  ducts  are  scat- 
tered somewhat  generally  throughout  the  wood  of  the  spring 
and  summer  growth  (Fig.  318).  Among  the  commonest  and 


TIMBER:  FORESTRY  393 

most  typical  of  the  ring-porous  woods  are  ash  and  oak,  and  of 
the  diffuse-porous  ones,  birch  and  maple. 

In  Figs.  316  and  317  the  lower  part  of  each  section  as  it 
stands  on  the  page  is  the  portion  nearest  the  pith  of  the  trunk 
from  which  it  came.  How  could  this  be  known  in  the  case  of 
Fig.  317?  Assuming  that  close  texture  (shown  by  the  darker 
shade  of  the  sections)  accompanies  slow  growth,  is  the  rate  of 
growth  the  same  throughout  the  season  ?  If  not,  in  which 
wood  is  it  most  nearly  the  same,  and  in  which  is  it  most  un- 
equal? If  the  pine  wood  shown  in  Fig.  316  is  (except  the 
resin  passages)  mostly  made  up  of  tracheids,  when  are  the 
largest  tracheids  formed  ? 

363*  Some  physical  properties  of  wood.  All  wood  contains 
moisture,  the  sapwood  or  outer  portion  more  than  the  heart- 
wood  or  inner  portion.  Not  all  of  this  water  can  be  driven 
off,  but  much  of  it  is  removed  by  seasoning  in  the  open  air, 
and  still  more  is  expelled  by  drying  lumber  in  kilns  at  a  tem- 
perature of  from  158°  to  180°  F.  Coniferous  woods  may  be 
placed  in  the  kiln  as  soon  as  sawed,  but  the  hard  woods  are 
usually  first  seasoned  in  the  air  for  from  three  to  six  months. 
The  loss  of  water  from  heartwood  during  kiln-drying  amounts 
to  from  16  to  60  per  cent  of  the  weight  of  the  green  lumber, 
the  amount  depending  on  the  kind  of  wood  treated. 

When  kiln-dried  the  heaviest  woods,  such  as  hickory,  oak, 
and  the  closest-grained  ash,  weigh  from  42  to  48  pounds  per 
cubic  foot.  Those  of  medium  weight,  such  as  southern  pine, 
sycamore,  and  soft  maple,  weigh  from  30  to  36  pounds  per 
cubic  foot.  The  very  lightest,  such  as  white  pine,  spruce,  and 
poplar,  weigh  from  18  to  24  pounds  per  cubic  foot.  Since 
water  weighs  about  62 J  pounds  per  cubic  foot,  all  of  our 
native  woods  float  when  dry,  though  some  of  them  sink 
when  green.  •  . 

Wood  is  a  very  strong  material  in  proportion  to  its  weight. 
A  piece  of  hickory,  good  oak,  or  long-leaf  pine,  1x1  inch  and 
12  inches  long  (loaded  in  the  middle  and  supported  at  both 
ends)  requires  a  weight  of  about  720  pounds  to  break  it. 


394  PRACTICAL  BOTANY 

A  stick  of  hickory  1x1  inch  is  pulled  apart  lengthwise  by 
a  load  of  32,000  pounds,  and  crushed  by  a  weight  of  8500 
pounds.  The  corresponding  values  for  long-leaf  pine  are 
17,300  pounds  and  7400  pounds. 

364.  Advantages  of  wood  over  other  structural  materials.1 
Certain  disadvantages  of  wood  for  construction  purposes,  such 
as  its  combustibility,  and  liability  to  decay,  are  readily  evident. 
Some  of  its  advantages  are  as  follows : 

(1)  Wood  is  far  cheaper  than  metals ;  bulk  for  bulk,  it  does 
not  on  the  average  cost  more  than  one  thirtieth  the  price  of 
iron  or  steel. 

(2)  Wood  is  much  more  easily  worked  than  metals. 

(3)  Weight  for  weight,  some  wood  is  stronger  than  iron 
or  steel.    A  bar  of  hickory  will  stand  a  stronger  pull  length- 
wise than  one  of  wrought  iron  of  equal  length  and  weight.    A 
block  of  the  best  hickory  or  long-leaf  pine  will  bear  without 
crushing  a  greater  load  than  a  block  of  wrought  iron  of  the 
same  height  and  weight. 

(4)  Wood  is  light,  and  therefore  much  more  convenient 
than  metals  for  many  purposes  of  construction,  from  build- 
ing vehicles  to  making  packing  cases,  and  for  tool  handles 
and  so  on. 

(5)  Wood  is  a  poor  conductor  of  heat,  and  on  this  account 
is  valuable  in  the  construction  of  houses,  railway  cars,  refrig- 
erators, and  other  things.    Even  in  buildings  or  sailing  craft- 
composed  largely  of  steel  it  is  therefore  found  highly  desirable 
to  make  the  floors,  decks,  and  much  of  the  interior  construc- 
tion of  wood. 

(6)  Wood  is  a  poor  conductor  of  electricity.    This  makes 
it  far  easier  to  manage  electric  wiring  in  houses  or  other  build- 
ings in  which  the  floor  joists  and  most  of  the  interior  finish 
consists  of  wood,  than  in  metal  structures. 

(7)  Wood  usually,  when  properly  finished,  has  a  highly 
ornamental  surface.  This  makes  it  possible  to  give  a  decorative 

i  See  Roth,  A  First  Book  of  Forestry,  pp.  232-238.  Ginn  and  Company, 
Boston. 


TIMBER:  FORESTRY  395 

effect  to  the  interiors  of  rooms,  railway  cars,  and  so  on,  fin- 
ished  with  wood,  which  could  be  obtained  with  other  materials 
only  with  much  difficulty  and  expense.  It  is  difficult  to  imag- 
ine how  beautiful  furniture  of  moderate  price,  such  as  is  made 
from  our  ornamental  woods,  could  be  made  from  any  metal. 

365.  Wood  as  fuel.   Although  coal  is  the  fuel  of  the  world's 
great  industries,  yet  there  are  large  areas  throughout  which 
wood  is  still  the  principal  fuel.    All  kinds  of  wood  can  be 
burned,  but  for  certain  purposes  those  kinds  are  preferred 
which  make  an  abundant  flame,  or  which  leave  solid  beds  of 
glowing  coals.    In  general  the  heating  effect  of  well-dried 
wood  when  burned  is  nearly  (though  by  no  means  exactly) 
proportional  to  its  weight  per  cubic  foot.    The  fuel  value  per 
cord  is  therefore  somewhat  dependent  on  the  weight  per  cord, 
and  the  heaviest  woods,  such  as  hickory,  sugar  maple,  most 
of  the  oaks,  hackberry,  and  some  kinds  of  ash,  are  the  best  .for 
burning.    For  certain  purposes  where  a  concentrated  smoke- 
less fuel  which  lights  easily  and  does  not  readily  go  out  is 
required,  charcoal  is  employed.   Generally  the  heaviest  woods 
make  a  dense  charcoal  of  great  heating  power. 

366.  Forestry.    Forestry  is  the  art  of  forest  management. 
It  should  be  based  on  the  scientific  study  of  woodlands.    This 
study  may  cover  all  such  topics  as  the  distribution  of  forests 
over  the  earth's  surface,  their  dependence  on  soil  and  climate, 
and  their  own  influence  upon  these.    It  also  discusses  their 
composition  as  plant   communities,1  their  progress  from   in- 
fancy, through  youth  and  maturity,  to  old  age,  and  their  rela- 
tions to  the  animal  world.    The  utility  of  forests  as  sources 
of  timber  is  a  forestry  topic  which  stands  foremost  in  the 
estimation  of  the  public. 

It  is  evident  that  forestry  is  so  extensive  a  subject  that  in 
a  portion  of  a  chapter  like  the  present  one  only  a  few  of  its 
most  important  subdivisions  can  be  briefly  discussed.  Every 
well-informed  person  should  at  least  know  in  a  general  way 
what  forestry  is,  since  the  maintenance  of  some  of  our  best 

i  See  Sect.  447. 


396 


PRACTICAL  BOTANY 


wooded  areas  and  the  creation  of  tracts  of  woodland  in  por- 
tions of  the  naturally  treeless  regions  have  become  matters  of 
national  importance. 

367.  Our  timber  supply  in  early  times.    At  the  time  of  the 
discovery  of  America,  and  until  long  after  the  Revolution, 
much  of  the   territory  now  included  in  the  United  States 
was  among  the  most  densely  wooded  portions  of  the  north 

temperate  zone.  No  other 
temperate  region  of  equal 
extent  possesses  so  great  a 
diversity  of  dicotyledonous 
trees,  and  gymnospermous 
trees  are  also  very  abundant. 
Along  almost  the  entire  At- 
lantic coast,  and  inland  to 
what  are  now  the  states  of 
Illinois  and  Minnesota,  tim- 
ber for  every  kind  of  con- 
struction was  once  to  be  had 
at  an  extremely  low  price. 
The  prevalence  in  early  times 
of  log  houses,  the  enormous 
beams  of  which  old  houses  in 
the  northeastern  states  are 
framed,  the  panels  of  white 
pine,  often  of  single  boards 
three  or  more  feet  wide,  without  a  knot,  and  occasionally  in 
the  Middle  West  the  fence  made  of  split  rails  of  black  walnut, 
—  all  testify  to  the  superabundance  of  timber  in  early  days. 

368.  Decrease  in  the  supply.    In  the  days  of  the  pioneers 
the  extensive  forests  were  serious  hindrances  to  the  settlement 
of  the  country.   They  harbored  wild  beasts  and  Indians,  they 
made  road-building  difficult  and  farming  at  first  almost  im- 
possible, and  they  sheltered  great  malaria-breeding  swamps. 
Naturally  the  first  step  in  rendering  the  new  country  habit- 
able was  to  make  clearings.   Trees  were  girdled  by  thousands, 


FIG.  319.  Primeval  deciduous  mixed 
forest,  —  maple  and  beech 


TIMBER:  FORESTRY 


397 


and  as  the  roots  soon  died  of  starvation  (Sect.  73),  they 
decayed,  and  the  trees  fell  and  were  burned.  In  this  way  the 
farms  continually  encroached  upon  the  woodlands,  until  areas 
of  primeval  forest  (Figs.  319  and  320)  became  so  rare  that 
few  of  us  have  ever  seen  one.  Lumbering  operations  which 
at  first  dealt  only  with  full-grown  trees,  often  centuries  old, 
came  to  deal  with  "  second-growth  "  woods,  in  which  many  of 


FIG.  320.   Uiidrained  deciduous  swamp  forest,  —  ash,  elm,  and  gum 

the  trees  were  hardly  more  than  saplings.  In  some  cases  the 
states  in  which  lumbering  was  once  an  extensive  industry  now 
import  most  of  their  good  lumber,  part  of  it  from  the  Pacific 
coast.  In  the  future  far  more  care  must  be  taken  to  maintain 
our  existing  timber  lands  and  to  plant  new  areas.  Lumber 
must  hereafter  be  partially  replaced  in  construction  work  by 
other  materials.  That  which  is  used  in  situations  where  it  is 
subject  to  rapid  decay,  as  in  fence  posts  and  railroad  ties,  must 
be  treated  with  chemicals  which  will  protect  it  from  the  attacks 
of  the  saprophytic  fungi  which  cause  wood  to  rot. 


FIG.  321.  Self -pruning  in  pure  growth  of  white  pines 

All  the  lower  limbs  are  dead  and  will  fall,  so  that  the  places  from  which  they 

grew  will  become  covered  with  new  wood.  Photograph  furnished  by  Connecticut 

Agricultural  Experiment  Station 


TIMBER:  FORESTRY  399 

369.  Composition  of  the  forest.1   Forests,  whether  of  conif- 
erous or  of  dicotyledonous  trees,  may  be  either  pure  or  mixed. 
A  pure  forest  is  one  which  consists  almost  entirely  of  a  single 
kind  of  tree;  a  mixed  forest,  one  which  contains  two  or  more  kinds. 
Nearly  pure  forests  of  white  pine  (Fig.  321)  and  of  long-leaf 
pine    (Fig.  260)    are   not   uncommon.    Few   kinds   of  North 
American  hard  woods  grow  unmixed  with  other  species  of 
trees,  but  some  of  our  birches,  oaks,  and  maples  occasionally 
do  so. 

Mixed  forests,  however,  are  the  rule,  and  these  may  consist  of 
only  two  or  three  kinds  of  trees,  as  beeches  and  maples ;  oaks 
and  hickories ;  oaks,  elms,  and  ashes.  Often  many  species  of 
several  genera  grow  side  by  side,  as  sycamores,  oaks,  ashes, 
black  walnuts,  elms,  and  hackberries,  which  occur  in  some  rich 
bottom  lands  of  the  Middle  West. 

Beneath  the  crowns  of  the  trees  many  kinds  of  shrubs  and 
undershrubs  often  flourish,  and  under  these  grow  herbaceous 
plants  in  greater  or  less  abundance.  Their  numbers  depend 
on  several  factors,  such  as  the  light  supply,  the  moisture 
supply,  and  the  fertility  of  the  soil.  In  the  eyes  of  the  for- 
ester many  of  these  plants  which  grow  beneath  the  trees  are 
weeds,  which  more  or  less  effectually  hinder  the  growth  of 
seedling  trees. 

370.  Tolerant  and  intolerant  trees.  A  tree  which  can  endure 
a  good  deal  of  shade  is  said  to  be  tolerant.    Examples  are, 
among  conifers,  the  hemlock  and  the  red  spruce ;  among  hard 
woods,  beech  and  maple.   Trees  which  require  much  light  are 
said  to  be  intolerant.   Examples  are,  among  conifers,  the  white 
pine  and  the  larch;  among  hard  woods,  oaks,  hickories,  and 
chestnuts.    As  a  rule,  seedlings  require  far  less  light  to  begin 
life  than  is  needed  to  enable  the  mature  tree  to  reach  its  maxi- 
mum size.   So  it  often  happens  that  seedling  trees  may  struggle 
on  for  years  on  the  forest  floor,  making  but  little  growth  until 
the  decay  and  fall  of  overshadowing  trees,  their  destruction 

1  This  section  applies  especially  to  forests  of  temperate  zones,  those  of 
tropical  climates  being  often  very  complex  in  their  make-up. 


400 


PRACTICAL  BOTANY 


by  wind,  or  their  being  felled  by  the  lumber- 
man, enables  the  seedling  to  grow  up  rapidly 
into  a  large  tree.  Properly  to  show  this  change 
in  rate  of  growth  would  require  a  series  of  pho- 
tographs taken  at  intervals  of  several  years, 
with  increasing  amounts  of  light  supplied  to 
the  young  tree;  but  there  is  often  a  most 
interesting  record  of  changed  rates  of  growth 
in  the  wood  of  the  trunk  itself  (Fig.  322). 

The  behavior  of  trees  as  regards  tolerance 
of  shade  has  to  be  carefully  considered  by  the 
forester,  since  he  must  not  try  to  start  seed- 
lings in  places  where  they  cannot  continue 
to  grow.  White  pines  would  not  succeed 
under  the  shade  of  hemlocks,  but  the  hem- 
locks can  grow  under  pines  and  may  thus 
succeed  them  in  a  wood  lot.1 

371.  Problems  of  forestry.  Forestry  has  to 
do  chiefly  with  tree  planting  on  unforested 
areas,  and  with  the  maintenance  of  existing 
forests  in  the  most  productive  condition.  Suc- 
cessful management  requires  much  attention 
to  the  choice  of  desirable  kinds  of  trees  for 
planting,  adapted  to  the  region  where  they  are 
to  grow.  Single  trees  or  portions  of  the  forest 
should  be  selected  when  in  suitable  condition 
to  be  felled.  Standing  timber  must  be  pro- 
tected from  all  kinds  of  destructive  agencies, 
such  as  forest  fires  and  animal  or  plant  para- 
sites. Felled  trees  must  be  protected  from 
decay  and  from  attacks  of  boring  insects,  and 
the  most  economical  methods  must  be  chosen 
for  felling,  transporting,  and  working  up  the 
various  kinds  of  timber. 

1  See  Pinchot,  "A  Primer  of  Forestry,"  Part  I,  Bul- 
letin 24,  Division  of  Forestry,  U.  S.  Dept.  Agr. 


_ 


FIG.  322.  Effect 
of  thinning  out 
on  forest  growth 

Part  of  the  cross 
section  of  a  fir 
tree,  about  half 
natural  size ;  the 
early  growth  from 
a  to  b  was  very 
slow,  as  the  young 
tree  was  shaded 
by  spruces;  from 
6  to  c  the  growth 
was  more  rapid,  as 
part  of  the  spruces 
were  blown  down 
by  a  storm  in  1871; 
from  c  to  d  the 
growth  was  still 
more  rapid,  as  the 
remaining  spruces 
were  destroyed  by 
a  storm  in  1885- 
1886.  After  Hop- 
kins, Division  of 
Entomology,  U.  S. 
Dept.  Agr. 


^ 


FIG.  323.  Young  pines  starting  in  partial  shade  of  hard- wood  trees 
Photograph  furnished  by  Connecticut  Agricultural  Experiment  Station 


401 


402 


TIMBER:  FORESTRY  403 

372.  Propagation  of  forest  trees.  In  wooded  regions,  where 
labor  is  expensive,  it  does  not  usually  pay  to  plant  large 
areas  with  seeds  of  trees,  or  to  set  out  many  young  seedlings. 
Self-sown  trees  will  usually  spring  up  in  natural  or  artificial 
openings  in  the  woods  (Figs.  323  and  324).  The  seeds  of  coni- 
fers are  blown  considerable  distances  by  the  wind,  and  those 
of  some  deciduous  trees,  such  as  birches,  elms,  ashes,  and 
maples,  are  carried  in  the  same  way.  Nuts  and  acorns,  on  level 
ground,  must  depend  largely  on  birds 
and  squirrels  as  carriers  (Fig.  325). 


FIG.  325.  Tree  planting  by  animals 

The  figure  represents  acorns  hoarded  by  a  chipmunk  in  a  prostrate  hollow  limb 
of  a  tree.  The  acorns  have  begun  to  grow,  and  one  or  more  of  them,  if  left  undis- 
turbed, would  doubtless  have  grown  into  trees.  From  photograph  by  R.  E.Webster 

Many  trees,  as  oaks,  chestnuts  (Fig.  326),  and  birches, 
sprout  freely  from  the  stump  and  thus  renew  woodlands,  after 
cutting,  much  more  quickly  than  growth  of  young  trees  from 
the  seed  could  accomplish  it.  Often  it  is  found  most  profit- 
able to  allow  the  sprouts  to  grow  only  twenty  or  thirty  years, 
forming  a  coppice  woodland,  which  is  then  cut  and  used  for 
making  telegraph  poles,  fence  posts,  railroad  ties,  and  so  on. 

373.  Tree  planting.  In  such  treeless  regions  as  the  prairies 
and  the  Great  Plains  it  is  often  desirable  to  establish  belts 
of  timber  or  considerable  tracts  of  woodland.  This  is  done 
partly  for  shelter  from  winds  and  partly  for  the  timber  pro- 
duced for  local  uses.  The  seeds  may  be  planted  where  the 


FIG.  326.  Chestnut  sprouts  springing  from  the  parent  stump 
Photograph  furnished  by  Connecticut  Agricultural  Experiment  Station 


404 


TIMBER:  FORESTRY 


405 


trees  are  finally  to  stand,  or  young  seedlings  may  be  procured 
from  a  forest  nursery.  The  latter  plan  is  the  better,  and  it  is  well 
to  have  the  young  seedlings  transplanted  once  or  twice  before 
their  final  planting,  to  avoid  formation  of  long  roots,  cutting 
of  which  would  check  the  growth  of  the  tree.  Both  coniferous 
and  dicotyledonous  trees  are  much  planted.  Some  of  the  most 
generally  available  conifers  are  several  kinds  of  spruce,  the 


FIG.  327.  A  four-year-old  plantation  of  hardy  catalpa 

At  the  left  are  Russian  mulberry  trees  of  the  same  age.   Note  the  dense  shade, 

sufficient  to  protect  the  forest  floor  from  weeds.   These  trees  were  cultivated  for 

three  years,  but  now  need  no  further  care  except  pruning 

white  pine,  the  Scotch  pine,  and  the  Austrian  pine.  Among  the 
desirable  dicotyledons  are  cottonwood,  silver  or  white  maple, 
green  ash,  honey  locust,  hardy  catalpa  (Fig.  327),  red  oak,  and 
(in  the  warmer  parts  of  the  country)  eucalyptus.  In  climates 
such  as  that  of  the  lowlands  of  California,  Eucalyptus  globulus 
is  the  most  rapid  growing  of  hard  woods,  reaching  a  diameter 
of  one  foot  and  a  height  of  125  feet  in  ten  years.  To  reach 
this  diameter  the  white  oak  would  take  a  hundred  years. 


406  PRACTICAL  BOTANY 

374.  Influence  of  forests  on  climate  and  water  supply.  The 

temperature  and  rainfall  in  and  near  forests  are  thought  to 
have  slightly  different  values  from  those  obtained  in  treeless 
areas,  but  the  amount  of  the  differences  is  not  fully  settled. 
The  effect  of  woods,  or  even  belts  of  trees,  as  windbreaks  is 
familiar  enough  to  every  one  who  has  traveled  along  a  road 
through  land  partly  wooded  and  partly  open  on  a  windy 
winter  day.  Evergreen  conifers  are,  of  course,  much  more 
serviceable  than  deciduous  trees  as  a  protection  against  winter 
storms,  and  they  are  much  planted  for  this  purpose  in  belts 
in  the  more  northerly  plains  and  prairie  states. 

The  greatest  service,  however,  which  is  rendered  by  wood- 
lands, next  perhaps  to  their  use  as  sources  of  timber,  is  in 
preventing  the  water  which  falls  as  rain  or  snow  from  running 
off  at  once  into  streams,  thus  causing  floods  which  are  fol- 
lowed by  long  periods  of  low  water.  The  run-off,  even  in  a 
grassy  prairie  country,  during  and  after  rains  is  very  rapid, 
so  that  streams  may  be  overflowing  their  banks  in  a  few  hours 
after  the  beginning  of  a  heavy  rain.  In  a  region  where  the 
land  is  mostly  tilled,  with  little  woodland,  the  run-off  is  still 
more  rapid,  so  that-  a  great  deal  of  the  water  precipitated  on 
a  hundred-acre  field  may  have  found  its  way  into  ditches  or 
watercourses  outside  of  its  limits  within  much  less  than  an 
hour  after  it  fell.  In  treeless  regions,  as  every  prairie  boy 
knows,  many  stream  beds  in  summer  become  merely  a  suc- 
cession of  pools  or  are  dry  throughout  their  length.  On  the 
other  hand,  the  forest  floor  is  often  moss-carpeted,  strewn 
with  leaves  and  covered  with  underbrush,  and  overlies  a  rich 
black  soil  containing  much  partially  decayed  animal  and  vege- 
table matter  known  as  humus,  which  is  penetrated  to  a  depth 
of  many  feet  by  an  intricate  network  of  rootlets.  This  soil 
retains  the  water  from  melting  snows,  often  for  weeks,  and 
holds  the  heaviest  rains  for  long  periods.  The  water  gradu- 
ally drains  off  along  the  surface  or  travels  slowly  through  the 
deep,  porous  soil,  gradually  finding  its  way  into  the  streams. 
It  is  therefore  of  the  highest  importance  that  such  regions  as 


TIMBEEi  FOKESTEY 


407 


the  White  Mountains,  the  Adirondacks,  the  central  and  south- 
ern Appalachians,  and  western  mountain  ranges  which  are 
used  as  sources  of  water  for  irrigation  should  be  forested.1 

375.  Forest  growth  prevents  erosion.  Along  with  the  value 
of  the  forest  in  regulating  the  flow  of  streams,  account  must  be 
taken  of  its  importance 
in  preventing  the  wash- 
ing away  or  erosion 
of  the  earth's  surface. 
Not  only  mountain  and 
hillsides  but  cultivated 
slopes  everywhere  are 
subject  to  great  losses  by 
washing  during  thaws 
after  snows  and  during 
rainstorms.  How  much 
earth  is  thus  annually 
carried  to  the  Gulf  by 
the  Mississippi  alone 
has  already  been  stated 
(Sect.  29).  Fig.  345 
represents  a  newly 
cleared  slope  under 
cultivation,  and  Fig. 
346  an  early  stage  in 
the  formation  of  gul- 
lies on  a  steeper  elope 
after  clearing.  The 
land  in  the  latter  case 

is  already  past  the  stage  in  which  it  can  be  cultivated  in  the 
ordinary  way.  Left  to  itself  the  tendency  is  for  the  washing 
to  continue  until  the  hillside  becomes  a  series  of  miniature 
ravines,  strewn  with  bowlders  and  separated  by  bare  ridges. 
Thousands  of  acres  in  the  southern  United  States  and  hundreds 

1  See  Fernow,  "  Forest  Influences,"  Bulletin  7,  Division  of  Forestry,  U.  S. 
Dept.  Agr. 


FIG.  328.  How  the  forest  holds  the  soil 

The  river  in  the  foreground  often  overflows  its 
banks,  but  little  erosion  occurs 


408  PRACTICAL  BOTANY 

of  thousands  in  some  of  what  were  once  the  most  fertile  parts 
of  southern  Europe  have  been  ruined  in  this  way.  Such  de- 
struction may  be  prevented  by  retaining  hillsides  in  a  wooded 
condition,  or  at  least  leaving  belts  of  trees  at  intervals,  run- 
ning at  right  angles  to  the  lines  of  slope.  The  early  stages  of 
erosion  may  be  checked  by  damming  the  principal  gullies  with 
logs,  stones,  and  brushwood,  and  then  replanting  with  suit- 
able trees  and  bushes.  Contour  plowing,  —  that  is,  plowing 
around  the  hill  instead  of  up  and  down  it,  —  terracing,  ditch- 
ing at  right  angles  to  the  lines  of  slope,  and  underdraining 
all  help  to  prevent  erosion. 

376.  Rules  for  forest  management.  For  a  detailed  account 
of  the  mode  of  keeping  up  the  productiveness  of  woodlands 
and  of  handling  timber  one  must  go  to  special  treatises  on 
forestry.1  In  this  place  there  is  room  only  to  name  a  very 
few  of  the  things  to  which  the  forester  or  manager  of  timber- 
lands  must  attend : 

(1)  A  timber  forest,  or  woodland,  consisting  in  considerable 
part  of  full-grown  trees,  should  be  cut  over  on  a  selective 
plan;  that  is  to  say,  only  those  trees  should  be  felled  which 
are  nearly  or  quite  full-grown,  or  which  are  too  much  crowded 
or  in  some  way  imperfect  or  diseased.    This  kind  of  selection 
may  not  be  possible  in  case  the  location  of  the  forest  is  rather 
inaccessible,  so  that  large  gangs  of  men  must  be  taken  into 
the  woods  and  the  cutting  all  done  within  a  limited  season. 
As  far  as  possible  the  felling  must  be  so  managed  that  promis- 
ing young  trees  are  not  barked  or  otherwise  injured  by  the 
falling  trunks  of  the  trees  which  are  cut. 

(2)  In  managing  coppice  woods  the  trees  must  be  cut  as 
soon  as  they  reach  a  merchantable  size,  usually  in  from  twenty 
to  forty  years. 

(3)  During  the  period  of   most  active  growth  all  wood- 
lands should  be  kept  covered  with  a  reasonably  close  stand, 
so  as  to  secure  self -pruning  and  not  encourage  the  growth  of 

1  For  elementary  principles,  see  Roth,  First  Book  of  Forestry.  Ginn 
and  Company,  Boston. 


TIMBER:  FORESTRY  409 

much-branched  trees  like  those  shown  in  Figs.  329  and  330, 
which,  when  cut  up  into  lumber,  will  be  very  full  of  knots. 
(4)  Forest  fires  must  be  prevented,  especially  in  woods 
of  coniferous  trees.  No  fires  for  any  purpose  should  ever  be 
kindled  during  dry  weather  in  the  heart  of  such  woodlands, 
except  in  moderately  large  clearings  free  from  brush.  Cutting 
up  large  tracts  of  forest  into  smaller  portions  by  means  of 


FIG.  329.  An  Austrian  pine  with  limbs  broken  by  clinging  snow 
This  shows  the  branching  habit  of  pines  grown  in  the  open,  worthless  for  timber 

roads  helps  to  keep  small  fires  from  spreading.  But  in  warm, 
dry  weather  a  coniferous-forest  fire  under  full  headway  is 
seldom  stopped  until  it  reaches  extensive  clearings,  or  rivers 
or  other  large  bodies  of  water. 

(5)  Parasitic  fungi  and  the  saprophytic  kinds  which  cause 
the  decay  of  fallen  trunks  and  branches  or  felled  trees  (Figs. 
208  and  209)  should  be  burned  when  to  do  so  is  not  too  ex- 
pensive, if  this  can  be  managed  without  danger  of  starting 
forest  fires. 


410 


PRACTICAL  BOTANY 


(G)  Wood-boring  and  leaf-eating  insects  should  be  killed, 
if  the  expense  of  the  process  is  not  too  great.  It  is  suggested, 
for  example,  that  the  great  damage  caused  by  the  spruce- 
destroying  beetle,  which  kills  mature  trees  by  mining  the  bark 


FIG.  330.  Oak  trees  growing  in  the  open 
A  white  oak  at  the  left  and  red  oak  at  the  right 

of  the  trunk,  may  be  much  lessened.  This  can  be  accom- 
plished by  cutting  and  removing  most  of  the  infested  trees,  or 
by  girdling  trees  early  in  June  to  expose  them  to  the  attacks  of 
the  beetles,  then  felling  and  either  peeling  them  or  immersing 


TIMBER:  FORESTRY  411 

them  in  water  to  destroy  the  insects  before  the  new  crop  of 
beetles  emerges  from  under  the  bark  the  following  June.1 

One  of  the  most  effectual  means  of  destroying  some  injuri- 
ous insects  consists  in  introducing  into  the  region  where  they 
abound  parasitic  or  other  insects  which  will  kill  great  numbers 
of  the  objectionable  species.  Plant  lice,  for  instance,  are  thus 
killed  by  ladybugs.  Vigorous  attempts  are  now  being  made 
to  exterminate  the  gypsy  moth  in  New  England  by  means  of 
parasites  and  by  carnivorous  insects  which  attack  and  kill  the 
moth  at  some  stage  of  its  existence.  The  caterpillars  of  this 
moth  are  extremely  destructive  to  many  kinds  of  trees,  which 
they  strip  of  their  leaves  in  a  short  time.  More  than  $1,000,- 
000  have  probably  been  expended  in  Massachusetts  alone  in 
trying  to  get  rid  of  this  pest.  The  moth  was  introduced  into 
America  in  1869  by  a  scientist  who  lived  at  Medford,  near 
Boston,  in  the  course  of  some  most  unfortunate  experiments 
on  silk-producing  insects.2 

(7)  Cattle  should  not  be  pastured  in  woods  in  which  it 
is  important  to  protect  the  growth  of  young  seedling  dicoty- 
ledonous trees.  They  do  not  greatly  injure  mature  trees. 
Sheep  pasturing  and  forestry  cannot  thrive  together,  since  by 
browsing  the  sheep  destroy  many  young  seedling  trees.  On 
grassy  hill  and  mountain  sides  sheep,  by  close  grazing  and  by 
cutting  the  turf  to  pieces  with  their  sharp  hoofs,  soon  kill  the 
grassy  cover  and  pave  the  way  for  extensive  erosion.  Great 
damage  has  been  done  in  this  way  in  the  Rocky  Mountain 
and  the  Pacific  slope  regions  of  our  own  country.  In  south- 
ern Europe  pasturing  sheep  and  goats  has  led  to  the  conver- 
sion of  great  areas  of  comparatively  fertile  mountain  sides 
into  bare  ridges  and  bowlder-lined  torrent  beds. 

1  See  " Insect  Enemies  of  the  Spruce  in  the  Northeast,"  Bulletin  28,  New 
Series,  Division  of  Entomology,  U.  S.  Dept.  Agr. 

2  "The  Gypsy  Moth  in  America,"  Bulletin  11,  New  Series,  Division  of 
Entomology,  U.  S.  Dept.  Agr. 


CHAPTER  XXIII 
PLANT  BREEDING 

377.  What  is  plant  breeding?  Plant  breeding  means  the 
intentional  production  and  perpetuation  of  new  and  especially 
desired  varieties  of  plants.    As  a  science  it  is  not  much  more 
than  fifty  years  old.    But  some  plants  have  been  cultivated  for 
over  forty-five  centuries,1  and  during  all  that  time  more  or 
less  attention  has  been  paid  to  choosing  and  keeping  up  desir- 
able varieties  of  plants. 

378.  Selection  of  spontaneous  varieties.  Plants  in  a  state  of 
nature  produce  many  varieties  by  ordinary  variation,  and  they 
may  occasionally  produce  new  species  by  the  kind  of  extensive 
and  abrupt  change  which  is  known  as  mutation. 

Only  a  very  few  of  all  the  multitude  of  spontaneous  vari- 
ations among  plants  are  likely  to  be  valuable  to  man.  An 
example  of  this  is  afforded  by  the  results  obtained  by  the 
discoverer  of  the  Concord  grape.  This  familiar  grape  was  a 
seedling  from  a  rather  promising  wild  variety.  The  original 
Concord  grape  is  so  valuable  on  account  of  its  productiveness 
and  hardiness  and  the  size  of  its  fruit  that  it  has  been  dissem- 
inated by  cuttings  over  a  large  part  of  the  United  States  and 
portions  of  Europe.  The  annual  world's  crop  of  this  variety 
is  now  exceedingly  large.  The  grower  of  the  Concord  mother 
vine  raised  more  than  22,000  seedlings  from  Concord  seeds, 
and  found  only  21  of  these  worthy  of  further  trial.  Not  one 
of  these  seedlings  is  now  a  well-known  grape. 

Most  farm  crops  afford  many  variations  in  the  same  field. 
These  variations  do  not  show  themselves  merely  in  slight  mat- 
ters of  proportion  or  size  of  organs,  —  details  interesting  only 
to  the  botanist ;  they  may  greatly  affect  the  economic  value  of 

1  See  De  Candolle,  Origin  of  Cultivated  Plants,  chap.  i 
412 


PLANT  BREEDING 


413 


the  plant.  In  the  case  of  timothy,  our  most  valuable  grass  for 
hay,  the  important  variations  concern  such  points  as  these  1 : 

(1)  Duration,  whether  annual  or  perennial. 

(2)  Power  to  spread  by  branches  from  the  base  of  the  stem 
(stolons),  some  plants  producing  10,  others  250  heads. 

(3)  Relation  of  seed  production  to  leaf  production,  —  some 
plants  leafy  and  making  good  pasture  but  bearing  little  seed. 

(4)  Yield,  —  single  plants  sometimes  producing  less  than 
J  pound  of  hay  and  others 

over  1J  pounds,  or  more 
than  five  times  as  much. 

379.  "  Coming  true  from 
the   seed."     Only,   careful 
trials  can  settle  the  ques- 
tion whether  in  any  given 
case  (as  in  that  of  timothy) 

variations  from  the   usual  **4Ba*'5tt£^sMBSii^^*t 

type  will  be  fully  trans- 
mitted from  the  seeds  of  a 
plant  to  the  offspring,  or, 
as  farmers  and  gardeners 
say,  will  "  come  true."  But 
there  is  enough  chance  of 
success  to  make  it  worth 

while  to  try  to  perpetuate  any  promising  new  plant  or  variation. 
The  reason  why  cultivated  plants  show  such  improvement 
over  their  wild  originals  (Fig.  331)  is,  in  the  case  of  those 
grown  from  seed,  because  desirable  modifications  in  these 
plants  have  occurred,  and  the  seed  of  the  improved  individuals 
has  been  saved  and  has  transmitted  the  improved  characteristics 
to  new  generations. 

380.  Variation  in  wheat.    Wheat  has  been  cultivated  in 
China  for  not  less  than  4600  years,  and  for  thousands  of  years 
many  varieties  have  been  grown  throughout  the  vast  tem- 
perate region  from  China  to  western  Europe.    It  is  thought 

1  See  Bailey,  Plant  Breeding.  The  Macmillan  Company,  New  York. 


FIG.  331.  Increase  in  size  of  the  potato 
tuber  due  to  cultivation 

The  upper  tuber  is  a  wild  one,  the  lower 

a  small  cultivated  tuber  of  the  Vermont 

variety.    Each  one  half  natural  size.   Wild 

potato  after  J.  Sabine 


414  PRACTICAL  BOTANY 

that  perhaps  the  wheat  plant  originated  in  the  once  highly 
fertile  portion  of  Turkey  in  Asia  between  the  Tigris  and  the 
Euphrates  rivers,  and  was  gradually  spread  by  cultivation 
both  eastward  and  westward  from  its  place  of  origin.1  About 
eight  species  of  wheat  are  recognized,  and  ths  number  of  vari- 
eties is  too  great  to  be  readily  counted.  In  view  of  the  great 
number  of  existing  varieties,  it  is  not  strange  that  there  are 
among  them  enough  types  to  suit  highly  unlike  soils  and  cli- 
mates. Accordingly  there  are  varieties  that  meet  the  needs  of 
the  soil  and  climate  of  Japan,  others  that  resist  the  drought 
and  cold  of  eastern  Russia  and  Manitoba,  others  still  that  can 
endure  the  drought  and  heat  of  southern  Russia  and  Turkes- 
tan, while  in  North  America  there  are  varieties  best  suited  to 
each  of  the  leading  wheat-growing  regions. 

Wheat  grown  anywhere  without  attention  to  the  selection 
of  pure  seed  is  likely  to  show  many  variations  in  the  same 
field,  —  a  fact  most  familiar  to  the  experts  in  our  agricultural 
experiment  stations.  In  the  early  part  of  the  nineteenth  cen- 
tury a  wheat  farmer  named  Le  Couteur,  living  in  the  Isle  of 
Jersey,  near  the  coast  of  France,  was  visited  by  Professor  La 
Gasca,  of  the  University  of  Madrid,  who  discovered  twenty- 
three  different  kinds  of  wheat  in  a  field  which  was  supposed 
to  be  all  nearly  alike.  Le  Couteur  was  much  impressed  by 
the  possibility  of  obtaining  desirable  new  breeds  of  wheat  by 
selecting  all  the  heads  of  each  of  the  best  types  found  in  the 
field  and  growing  each  type  by  itself  until  he  could  find  out 
all  necessary  details  about  its  productiveness  and  other  charac- 
teristics. In  this  way  he  obtained  several  new  varieties,  among 
them  one  excellent  kind  still  much  grown  in  England  and 
northern  France,  known  as  "Bellevue  de  Talavera."  This 
famous  wheat  comes  true  to  such  an  extent  that  no  other 
varieties  have  been  derived  from  it.2 

1  For  another  view  see  Bulletin  274,  Bureau  of  Plant  Industry,  U.  S. 
Dept.  Agr.,  1913. 

2  See  Hugo  de  Vries,  "Plant  Breeding"  ;  and  "Species  and  Varieties: 
their  Origin  by  Mutation."   The  Open  Court  Publishing  Co.,  Chicago. 


PLANT  BREEDING  415 

381.  Wheat  breeding:  its  purpose.  Wheat  is  the  most  im- 
portant grain  for  human  food  in  temperate  climates,  and  North 
America  is  by  far  the  greatest  wheat-producing  region  in  the 
world.    The  annual  value  of  the  crop  of  the  United  States 
ranges  from  $250,000,000  to  1500,000,000.    Scientific  wheat 
breeding  began  hardly  a  century  ago,   and  has   progressed 
more  in  the  United  States  since  1890  than  during  all  our 
previous  history. 

Some  desirable  qualities  to  be  sought  in  wheat  breeding  are 
(1)  large  yield  per  acre  ;  (2)  good  quality  for  bread  making, 
requiring  a  high  per  cent  of  the  tenacious  gluten,  the  main 
protein  portion  of  the  grain ;  (3)  hardiness,  shown  in  winter 
wheat,  in  resisting  severe  winter  conditions ;  (4)  resistance  to 
rust ;  (5)  resistance  to  drought. 

Not  all  of  these  qualities  can  be  combined  in  the  highest 
degree  in  any  one  variety,  and  therefore  every  region  should 
grow  the  particular  kind  of  wheat  best  suited  to  the  local 
conditions  and  market. 

382.  Wheac  breeding :  the  method.  In  order  to  show  how 
carefully  the  process  of  wheat  breeding  is  managed  in  our  best 
agricultural  experiment  stations,  the  principal  steps  of  the 
operation  are  here  given  in  the  barest  outline,  omitting  many 
most  important  details.1 

(1)  Ten  thousand  large,  sounu  kernels  of  a  single  good 
variety  of  wheat  are  selected,  planted  in  hills,  and  each  hill 
numbered.    About  95  per  cent  of  the  poorer  plants  are  re- 
jected as  they  mature.    The  heads  of  each  of  the  chosen  plants 
are  put  together  in  an  envelope  and  preserved.    When  thor- 
oughly dry  the  product  of  each  plant  is  weighed,  and  only  a 
few  of  the  heaviest  groups  of  heads  are  kept  for  seed. 

(2)  The  second  year  about  a  hundred  of  the  seeds  of  each 
mother  plant  are  planted  in  a  group  to  which  is  given  a  special 
designating  number  (hundred-group  or  centgener).    Heads  of 

1  See  Bulletin  62,  University  of  Minnesota  Agricultural  Experiment 
Station,  and  Bulletin  29,  Division  of  Vegetable  Physiology  and  Pathology, 
U.  S.  Dept.  Agr. 


416  PRACTICAL  BOTANY 

several  of  the  best  plants  in  each  hundred-group  are  reserved 
for  seed.  The  total  produced  by  each  hundred-group  is  weighed 
to  enable  the  experimenter  to  estimate  the  comparative  value 
of  the  mother  plants  of  (1). 

(3)  The  third  year  the  process  of  the  second  year  is  repeated. 

(4)  The  fourth  year  the  same  process  is  repeated. 

(5)  The  fifth  year  the  most  promising  varieties  are  planted 
in  small  fields  in  the  ordinary  way.    Those  varieties  which  yield 
abundantly  in  the  field  and  turn  out  well  in  the  milling  tests 
applied  to  the  harvested  grain  are  distributed  among  farmers 
for  seed  wheat. 

A  new  variety  can  soon  be  introduced  over  an  immense 
territory.  It  is  estimated  that  in  fifteen  years  from  the  time 
of  planting  one  seed,  its  descendants  might  be  made  to  cover 
more  than  5,000,000  acres  of  wheat  fields. 

Wheat  breeding  is  still  making  such  rapid  progress  that  it 
is  not  now  possible  to  say  how  much  the  quality  and  quantity 
of  our  wheat  crop  may  yet  be  improved  by  the  introduction 
of  better  varieties.  The  total  number  of  acres  in  the  United 
States  differs  considerably  from  year  to  year.  It  seems  likely, 
as  a  rule,  to  exceed  45,000,000  acres.1  The  average  yield 
ranges  between  10  and  15  bushels  per  acre,  although  it  is 
possible  with  the  most  improved  seed  on  the  best  soils  to 
raise  more  than  40  bushels  per  acre.2  Choice  of  the  best  seed 
would  undoubtedly  increase  the  average  yield  to  from  13  to 
at  least  18  bushels.  It  is  easy  to  see  how  important  a  gain 
this  would  be  if  it  were  calculated  in  terms  of  the  current 
price  of  wheat. 

383.  Principles  upon  which  wheat  breeding  depends.3  The 
work  of  Le  Couteur  and  of  a  Scotch  breeder  of  small  grains 
named  Patrick  Shirreff,  who  discovered  his  first  valuable 


1  See  Carleton,   "The   Future  Wheat   Supply  of  the   United  States," 
Science,  August  5,  1910. 

2  See  Hopkins,    Soil  Fertility  and   Permanent  Agriculture.    Ginn  and 
Company,  Boston. 

8  See  De  Vries,  Plant  Breeding.   Open  Court  Publishing  Co.,  Chicago. 


PLANT  BREEDING  417 

variety  of  wheat  in  1819,  was  not  based  on  any  general 
knowledge  of  the  laws  of  plant  variation  and  inheritance.  The 
principles  of  breeding,  as  applied  to  the  small  grains,  were 
first  worked  out  by  Professor  W.  M.  Hays  of  the  University 
of  Minnesota  Agricultural  Experiment  Station,  and  by  Dr. 
Hjalmar  Nilsson,  director  of  the  experiment  station  at  Svalof, 
Sweden.  Some  of  the  main  principles  upon  which  wheat 
breeding  depends  may  be  stated  as  follows : 

(1)  Every  species  of  cereal  usually  comprises  many  well- 
marked  varieties,  or,  as  they  are  sometimes  called,  elemen- 
tary species.    Sometimes  there  are  several  hundreds  of  these 
included  in  each  of  the  longest-cultivated  species  of  grain, 
notably  so  in  the  case  of  wheat. 

(2)  The  varieties  may,  while  still  growing  in  the  field,  be 
distinguished  by  such  botanical  characters  as  the  position, 
shape,  size,  and  bearded  or  beardless  condition  of  the  head ; 
the  form,  size,  and  appendages  of  the  spikelets  which  it  con- 
tains; and  the  size,  shape,  color,  and  hardness  of  the  grain.1 

(3)  The  varieties  distinguished  by  such  characters  as  are 
mentioned  in  (2)  often  differ  much  in  their  economic  value, 
depending  on  such  qualities  as  productiveness,  resistance  to 
drought,  resistance  to  rust,  and  the  grade  of  flour  which  they 
produce. 

(4)  Varieties  usually  come  true  from  the  seed,  so  that  when 
one  has  been  chosen  and  isolated  it  may  be  grown  indefinitely 
with  little  change. 

384.  Variation  in  corn.  Indian  corn  is  preeminently  an 
American  plant.  At  the  time  of  the  discovery  of  America, 
and  probably  for  a  long  period  before  that  time,  it  was  grown 
by  the  Peruvians,  the  Mexicans,  and  by  many  tribes  of  Indians. 
It  is  supposed  to  have  originated  in  South  or  Central  Amer- 
ica, near  the  west  coast.  The  corn  plant  differs  greatly  in  size 
and  in  the  time  required  for  maturing.  The  smallest  pop  corn 
is  1J-  feet  high,  while  field  corn  has  been  known  to  reach  a 

1  The  hardness  cannot  be  accurately  known  until  the  grain  is  ripe 
and  dry. 


418  PRACTICAL  BOTANY 

height  of  over  22  feet.  Some  corn  in  Paraguay  is  said  to  ripen 
in  one  month,  while  Illinois  field  corn  requires  from  four  to 
five  months.1 

Six  well-defined  types  of  corn  are  recognized,  but  only  four 
are  of  much  economic  importance.  These  are  pop  corn,  with 
small  kernels  and  endosperm  all  or  nearly  all  horn-like ;  flint 
corn,  with  much  horn-like  endosperm  and  a  grain  too  hard  to 
be  fed  to  most  animals  without  being  ground ;  dent  corn,  with 
the  kernels  indented  at  the  outer  end  :  and  sweet  corn,  in  which 


FIG.  332.   A  prize  ear  of  "  Johnson  County  White  "  corn2 
An  admirable  type  of  dent  corn.    Photograph  by  L.  B.  Clore 

most  of  the  starch  of  the  endosperm  is  replaced  by  a  kind  of 
sugar.  Of  these  four  kinds,  dent  corn  is  by  far  the  most  im- 
portant, constituting  the  great  bulk  of  the  crop  in  the  corn 
belt.  Each  of  the  types  of  corn  has  many  varieties ;  of  dent 
corn  alone  more  than  three  hundred  have  been  named  and 
described.  Most  of  these  varieties  are  found  to  show  slight 
variations,  which  make  them  more  or  less  desirable  for  the 
corn  grower,  and  his  efforts  must  be  directed  mainly  to  im- 
proving the  quality  of  existing  kinds. 

1  See  Bulletin  57,  Office  of  Experiment  Stations,  U.  S.  Dept.  Agr.,  1899. 

2  This  ear  of  corn  was  bid  in  by  the  grower  (Mr.  Clore)  at  an  auction  sale 
of  exhibits  at  the  Chicago  National  Corn  Exposition  in  October,  1907.   The 
price  paid  was  $250. 


PLANT  BREEDING 


419 


A  B 

FIG.  333.  Kernels  of  corn  with  high  and  with 
low  percentage  of  proteins 

A,  high  proteins ;  B,  low  proteins ;  p,  horny  layer, 
consisting  largely  of  proteins;  s,  white  starchy 
portion ;  e,  embryo.  After  Bulletin  87,  Univer- 
sity of  Illinois  Agricultural  Experiment  Station 


385.  Qualities  sought  by  the  corn  breeder.1  Of  the  many 
qualities  that  may  be  sought  by  the  corn  grower  it  will  be 
enough  here  to  mention  only  .four  of  the  most  important: 

(1)  productiveness ; 

(2)  high   percentage  . .  p.  _  ., 
of  proteins  ;  (3)  high 

percentage  of  oil;  (4) 
low  percentage  of  oil. 
With  reference  to 
(1)  it  suffices  here  to 
say  that  the  average 
yield  of  corn  for  the 
entire  United  States, 
according  to  statistics 
for  1908,  was  a  little 
over  26  bushels  per 
acre ;  for  the  New 
England  States,  with 
no  better  soil  and  a 
poorer  climate,  it  was 
40.5  bushels;  and  for 
some  New  England 
growers  it  was  100  or 
more  bushels  per  acre. 
No  small  part  of  the 
difference  between 
the  average  26-bushel 
yield  and  the  100- 
bushel  yield  depends 
on  the  choice  of  seed.2 
Greatly  increased  care 
in  its  selection  would 
probably  at  once  add 


FIG.  334.  Kernels  of  corn  with  high  and  witli 
low  percentage  of  oil 

A,Ai,  cross  section  and  face  view  of  high-oil  ker- 
nels ;  B,B\,  cross  section  and  face  view  of  low-oil 
kernels ;  e,  embryo.  Most  of  the  oil  (as  well  as  a 
good  deal  of  proteins)  is  contained  in  the  embryo, 
so  that  a  large  embryo  means  a  high  percentage 
of  oil  in  the  grain.  After  Bulletin  87,  University 
of  Illinois  Agricultural  Experiment  Station 


1  See  Bulletins  55,  82,  and  87,  Illinois  Agricultural  Experiment  Station. 

2  See  Massachusetts  Crop  Report,  May,  1910. 


420 


PRACTICAL  BOTANY 


more  than  $100,000,000  to  the  annual  value  of  our  corn  crop. 
The  structure  of  the  grain  of  corn,  as  shown  by  the  diagrams 
in  Figs.  333  and  334,  is  such  that  the  relative  amounts  of  pro- 
teins, starch,  and 
oil  can  be  esti- 
mated roughly 
by  a  mechanical 
examination  of 
the  grain.  This 
most  important 
fact  was  discov- 
ered by  Professor 
C.  G.  Hopkins,  of  the 
University  of  Illinois. 
The  proteins  are  largely 
stored  in  the  horn-like  part  of 
the  endosperm  (Fig.  333,  p)  and 
in  the  embryo;  the  starch  is  mainly 
found  in  the  white,  floury  part  of  the 
endosperm  («) ;  and  the  oil  is  nearly  all  in 
the  embryo  (e).  If  seed  corn  is  chosen  from 
ears  with  kernels  in  which  the  horn-like 
portion  is  highly  developed,  the  result  will 
be  to  secure  a  crop  with  a  large  percentage 
of  proteins ;  seed  corn  with  large  embryos 
will  yield  a  crop  rich  in  oil,  and  seed  corn 
with  small  embryos  a  crop  poor  in  oil. 

Corn  with  high  proteins  is  especially 
valuable  as  a  food  for  man  and  the  lower 
animals,  since  the  most  serious  fault  found 
with  corn  as  a  cereal  food  is  its  low  per- 
centage of  proteins  compared  with  its  oil 
and  carbohydrates.  Corn  with  high  oil  value  is  especially  de- 
sired by  the  glucose  manufacturers,  since  they  also  manu- 
facture corn  oil,  which  is  the  highest-priced  component  of  the 
grain.  Corn  with  a  low  percentage  of  oil  is  in  demand  for 


FIG.  335.  Part  of  a 
corn  tassel  (stami- 
nate  flower  cluster) 

6r,abract;  st,  stamens. 
One  half  natural  size 


PLANT  BREEDING 


421 


feeding  hogs  for  bacon, 
especially  for  exporta- 
tion. It  has  been  found 
possible,  at  the  Uni- 
versity of  Illinois  Ag- 
ricultural Experiment 
Station,  to  breed  low- 
protein  corn  with  an 
average  percentage  of 
6.7  proteins,  and  high- 
protein  corn  with  an 
average  percentage  of 
14.4  proteins.  At  the 
same  station  the  average 
low-oil  corn  contained 
2.5  per  cent  of  oil  and 
the  high-oil  corn  7.0  per 
cent.  The  process  of 
selection  must  be  kept 
up,  for  the  variations 
thus  obtained  are  not 
permanent  varieties. 

386.  Method  of  corn 
breeding.  It  may  be 
said  in  a  general  way 
that  the  method  of 
breeding  corn  is  based 
on  the  same  principles 
as  those  adopted  for 
wheat  and  other  cereals. 
There  are,  however, 
many  variations  in  de- 
tails, some  of  the  most 
important  depending  on 
the  fact  that  the  plants 
should  be  pollinated 


FIG.  336.  Structure  of  an  ear  of  corn  (pistil- 
late flower  cluster) 

A,  section  of  young  ear  before  fertilization  of  the- 
ovules  (grains) :  ax,  axis  of  spike  (cob) ;  si,  ends 
of  silk  (styles  and  stigmas).  B,  magnified  sec- 
tion through  a  grain,  showing  bracts  around  the 
ovary,  the  ovule  (o),  and  the  base  of  the  style; 
C,  upper  portion  of  style,  with  the  stigmas  (st) 
considerably  magnified.  After  F.  L.  Sargent 


422  PRACTICAL  BOTANY 

with  pollen  from  other  individuals,  but  that  these  should,  as  far 
as  possible,  all  be  of  the  same  stock.  It  is  not  sufficient  that 
all  should  be  of  the  same  variety ;  the  most  rapid  progress 
will  be  attained  if  all  the  parent  plants  are  descended  from 
the  same  ear  of  corn. 

It  will  not  be  necessary  to  give  in  detail  all  the  methods 
followed  in  the  selection  of  seed,  and  the  precautions  which 


FIG.  337.  Cross-pollination  and  self-pollination 

The  effect  of  cross-pollination  and  of  self-pollination  on  the  growth  of  corn  from 
the  seed.  The  two  rows  of  spindling  plants  at  the  left  grew  from  seed  produced  by 
self-pollination,  the  larger  plants  of  the  other  rows  from  seed  produced  by  cross- 
pollination.   Photograph  furnished  by  Funk  Bros.  Seed  Co. 

are  adopted  to  prevent  mixture  of  varieties  in  the  growing 
crop.    Successful  corn  breeding  demands: 

(1)  The  choice  of  the  most  desirable  known  variety  as  a 
basis  for  breeding  for  any  given  purpose. 

(2)  Selection  of  well-matured  ears  from  the  best  plants 
in  the  field. 

(3)  Growing  trial  rows  the  next  season  from  the  ears  of 
(2),  each  ear  planted  in  a  row  by  itself.    Every  other  row 
should  be  detasseled  to  prevent  the  plants  from  pollinating 


PLANT  BREEDING  423 

their  own  ears,  and  seed  ears  should  be  saved  only  from  the 
detasseled  rows. 

(4)  The  continuation  during  subsequent  seasons  of  the 
process  of  seed  growing  from  the  best  plants  obtained  in  (3). 

In  beginning  to  breed  corn  it  is  better  to  use  seed  obtained 
from  the  locality  in  which  the  experiment  is  to  be  made. 
That  grown  under  decidedly  different  conditions  may  not 
succeed.  If  high-  or  low-oil  corn  or  high-  or  low-protein  corn 
is  desired,  the  ears  used  for  seed  must  be  carefully  chosen 
with  reference  to  the  development  of  the  horn-like  endosperm 
or  of  the  embryo  (Figs.  333  and  334).  Selection  in  the  field, 
as  mentioned  in  (2),  is  necessary  in  order  to  insure  that  the 
ears  chosen  grew  on  vigorous  plants,  and  that  ears  from  the 
same  plant  are  kept  together.  If  detasseling  is  not  thoroughly 
carried  out,  much  self-pollination  and  self-fertilization  is  sure 
to  occur.  Corn  which  is  self -fertilized  produces  smaller  and 
less  vigorous  plants  the  next  season  than  cross-fertilized  corn 
(Fig.  337).  Detasseling  has,  therefore,  been  found  to  increase 
the  yield  of  corn  more  than  ten  bushels  per  acre.1 

387.  Williams's  method.  The  method  of  corn  breeding  as 
at>ove  outlined  has  been  criticized  on  the  ground  that  little  or 
no  attention  is  paid  to  the  productiveness  of  the  plant  used 
as  the  source  of  pollen.  A  new  sys.tem  devised  by  Professor 
C.  G.  Williams,  of  the  Ohio  Agricultural  Experiment  Station, 
provides  for  equally  careful  selection  of  the  staminate  and  of 
the  pistillate  parent.  The  system  in  its  barest  outlines,  as 
stated  by  Professor  Williams,  provides  for : 

1.  The  usual  ear-row  test.    Only  a  portion  (usually  about  one  half) 
of  each  ear  is  planted.    The  remnant  is  carefully  saved,  and  when  the 
ear-row  test  has  shown  which  ears  are  superior,  recourse  is  had  to  the 
remnants  to  perpetuate  these  ears. 

2.  An  isolated  breeding  plot  in  which  are  planted  the  four  or  five 
best  ears  as  demonstrated  by  1.  Not  the  progeny  of  the  best  ears,  but 

1  For  details  about  corn  breeding  see  De  Vries,  Plant  Breeding,  Open 
Court  Publishing  Co.,  Chicago;  Bulletin  100,  Illinois  Agricultural  Experi- 
ment Station  ;  and  Circular  66,  Ohio  Agricultural  Experiment  Station. 


424  PRACTICAL  BOTANY 

the  original  ears.  Usually  the  best  ear  is  used  for  staminate  plants  and 
planted  on  each  alternate  row  in  the  small  breeding  plot.  All  the  plants 
from  the  other  ears  going  into  the  plot  are  detasseled. 

The  pedigreed l  strains  produced  in  the  breeding  plot  are  multiplied 
for  general  field  use  and  also  furnish  ears  of  varying  worth  for  a  second 
ear-row  test,  if  it  is  desired  to  continue  the  improvement. 

The  ear-row  test  need  not  be  isolated,  for  no  seed  is  taken  from  it. 
Neither  is  there  any  need  for  detasseling  until  the  breeding  plot  is 
reached. 

388.  Sugar  beet  breeding.  Almost  all  the  sugar  that  is  used 
by  civilized  peoples  is  manufactured  from  sugar  cane  and 
sugar  beets,  the  latter  furnishing  the  greater  part  of  the  world's 
supply.  Beets  of  many  varieties  have  been  cultivated  since 
the  sixteenth  century  or  earlier.  But  it  was  only  as  late  as 
the  middle  of  the  nineteenth  century  that  scientific  efforts 
were  made  by  Louis  Vilmorin  to  increase  the  percentage  of 
sugar  in  beets  grown  for  sugar-making.  The  sweetest  roots 
are  usually  the  heaviest  in  proportion  to  their  bulk,2  and 
therefore  Vilmorin  tested  whole  beets  or  pieces  cut  from  them 
by  placing  them  in  brine  strong  enough  to  float  all  of  the 
roots  except  those  which  contained  an  unusually  large  per  cent 
of  sugar.  The  sugar  beet  is  ordinarily  (though  not  always) 
a  biennial,  and  the  root  produced  in  one  year  is  used  for  grow- 
ing seed  in  the  second  year.  These  selected  beets  were  planted 
for  seed  and  became  the  parents  of  valuable  new  races. 

At  present  the  process  of  producing  beets  of  the  highest 
value  for  the  manufacture  of  sugar  is  a  long  and  complicated 
one,  consisting,  as  usually  carried  out,  of  the  following  steps- 

(1)  Planting  the  best  seed  that  can  be  bought. 

(2)  Chemically  testing  average  samples  of  the  roots  that 
are  grown  from  the  seed  of  (1)  to  see  if  they  are  good  enough 
to  breed  from. 

(3)  Selecting  the  best  single  roots  by  a  chemical  test.  Less 
than  one  half  of  one  per  cent  of  all  the  beets  tested  pass  this 
examination  in  a  satisfactory  way. 

1  Pedigreed,  because  the  pedigree  on  both  sides  is  a  matter  of  record. 

2  That  is,  have  the  highest  specific  gravity. 


PLANT  BREEDING  425 

(4)  Planting  the  mother   roots   selected  in   (3)   for   the 
production  of  what  is  called  "elite  seed." 

(5)  Growing  from  elite  seed  small  beets  which  are  planted 
to  secure  commercial  seed. 

It  requires  five  years  to  obtain  seed  in  large  quantities  from 
the  very  few  selected  roots  with  which  the  process  of  securing 
improved  seed  is  begun.1 

Some  notion  of  the  thoroughness  with  which  European 
seed  growers  choose  their  beets  may  be  gathered  from  the 
fact  that  in  1889-1890  one  of  the  most  important  firms  tested 
2,782,300  roots,  from  which  it  selected  only  3043  to  be  planted 
for  seed  production.  Constant  pains  must  be  taken  in  main- 
taining the  best  possible  seed  supply,  as  the  quality  becomes 
lowered  at  once  when  the  seed  is  grown  without  special  pre- 
cautions. This  is  due  to  the  fact  that  the  variations  in  beets 
are  not  elementary  species  (Sect.  383),  and  therefore  are  not 
sure  to  come  true  from  the  seed.  Two  of  the  most  serious 
ways  in  which  a  poor  stock  of  sugar  beets  falls  short  are  in 
the  low  percentage  of  sugar  and  in  the  production  of  many 
worthless  annual  plants.  In  central  Europe  the  annual  indi- 
viduals sometimes  constitute  20  per  cent  of  the  entire  crop. 

The  average  yield  of  sugar  from  American-grown  beets  is 
at  present  12  per  cent  or  less.  Exceptional  beets  have  been 
found  to  contain  more  than  double  this  amount.  It  is  impos- 
sible at  present  to  produce  the  roots  in  large  quantities  with 
anywhere  near  this  high  percentage  of  sugar,  but  decided  gains 
may  easily  be  secured,  and  an  increase  of  2  per  cent  in  the 
yield  would  mean  a  gain  of  something  like  $  100,000  per  year 
in  the  beet-sugar  production  of  the  United  States. 

389.  Constant  and  inconstant  varieties.  Beets,  as  stated  in 
Sect.  388,  do  not  long  remain  true  to  type  unless  there  is  con- 
tinued selection  of  the  seed.  There  is  a  constant  tendency  of 
the  high-bred  sugar  beet  to  "  run  out,"  —  that  is,  to  revert  to 
the  average  sweetness  of  beets  grown  from  unselected  seed. 
In  this  respect  beets  differ  sharply  from  the  cereals,  most  of 
1  Sec  Yearbook  of  the  Department  of  Agriculture,  1904. 


426  PRACTICAL  BOTANY 

which  do  not  quickly  revert  to  the  original  type,  unless  as  a 
result  of  miscellaneous  crossing.  Plant  breeding,  as  a  science, 
is  much  too  young  to  enable  us  as  yet  to  answer  the  question 
how  far  varieties  tend  to  "  run  out "  and  what  plants  are  most 
subject  to  this  reversion.1  It  is  probable  that  most  cultivated 
plants  grown  from  seed  will  be  found  to  be  decidedly  less 
constant  in  maintaining  their  character  for  years  than  are 
the  grains. 

390.  Hybridizing.    Hybridizing,  as  the  term  is  now  gen- 
erally used,  means  the  production  of  seed  by  the  action  of  pol- 
len of  one  variety  or  species  on  the  ovule  of  another  variety  or 
species.    In  order  to  produce  seed  that  will  grow,  both  species 
must  usually  belong  to  the  same  genus.    Frequently  different 
species  of  the  same  genus  hybridize  with  difficulty;  that  is, 
the  result  of  the  attempted  cross  is  to  produce  no  seed,  or  seed 
that  does  not  grow  well.    The  offspring  produced  by  hybridi- 
zation are  known  as  hybrids. 

It  has  long  been  known  that  hybrids  are  often  extraordi- 
narily variable,  but  the  law  (Mendel's  law)  which  in  many 
cases,  though  not  in  all,  determines  their  characteristics  and 
their  mode  of  variation,  was  not  discovered  until  1865,2  and 
did  not  become  well  known  until  some  thirty-five  years  later. 

Recently  much  use  has  been  made  of  hybridizing  in  order 
to  set  plants  to  varying,  and  the  most  desirable  varieties  thus 
produced  have  then  been  selected  and  used  in  breeding  as 
already  described. 

391.  How  hybrids  are  artificially  produced.     Hybridizing, 
or  crossing  plants,  is  sometimes  an  easy,  sometimes  a  rather  dif- 
ficult, process.    It  is  simplest  in  unisexual  flowers,  for  exam- 
ple, in  those  of  Indian  corn.    Here  the  "tassel"  (Fig.  335)  is  a 
cluster  of  spikes  of  staminate  flowers,  and  the  "ear"  (Fig.  336) 
is  a  spike  of  pistillate  flowers,  each  thread  of  the  "  silk  "  rep- 
resenting a  stigma  and  style  attached  to  an  ovary  (grain  of 

1  See  Bailey,  The  Survival  of  the  Unlike,  Essay  XXIV.   The  Macmillan 
Company,  New  York. 

2  See  Bailey,  Plant  Breeding,  chap.  iv.  The  Macmillan  Company,  New  York. 


PLANT  BREEDING 


427 


corn).  In  hybridizing  corn  it  is  only  necessary  to  tie  a  paper 
bag  over  the  ear  before  the  silk  appears,  in  order  to  keep  off 
stray  pollen,  and  leave  it  covered  until  full-grown ;  then  re- 
move the  bag,  dust  the  silk  thoroughly  with  pollen  from  tas- 
sels of  the  desired  crossing  variety  of  corn,  and  thereafter  keep 
the  ear  covered  until  the  silk  is  entirely  withered.  Sometimes 
in  hybridizing  corn  the  stalks  are  detasseled  just  before  the 
ears  are  ready  to  receive  pollen.  If  all  the  stalks 
of  one  kind  or  one  row  are  thus  detasseled,  it 
is  made  probable  that  pollen,  if  received  at  all 
by  the  ears  of  the  detasseled  stalks,  must  come 

from  another  row 
or  another  kind  of 
corn.  The  detas- 
seling  of  alternate 
rows  is  a  rather 
common  mode  of 
insuring  cross-pol- 
lination. In  most 
cases  of  hybridiz- 
ing with  bisexual 
flowers  it  is  nec- 
essary to  carry  out 
processes  similar  to 
the  following  ones : 

(1)  Select  the  flower  to  be  pollinated  before  it  opens  or 
its  own  pollen  is  mature.    If  it  is  one  of  a  cluster  of  flowers, 
as  in  the  wheat  or  the  apple,  remove  from  the  cluster  of  the 
flowers  all  that  are  not  to  be  operated  on. 

(2)  Open  the  remaining  flowers  and  remove  the  stamens 
by  taking  hold  of  the  filaments  with  fine  forceps,  or  cut  away 
all  the  stamens  at  once,  as  shown  in  Fig.  338.   Then  cover  the 
flower  or  the  entire  twig  with  a  paper  bag  until  the  stigma 
is  mature. 

(3)  When  the  stigma  is  mature,  pollinate  it  with  the  de- 
sired kind  of  pollen.  This  may  be  done  with  the  finger  tip,  or 


FIG.  338.  A  peach  flower  prepared  for  hybridization 

A,  flower  cut  round  for  removal  of  the  stamens,  with 
the  removed  parts  of  the  young  flower  showing  above ; 

B,  longitudinal  section  of  a  flower  showing  level  (s) 

at  which  the  cut  was  made  in  A 


428 


PRACTICAL  BOTANY 


with  a  cameFs-hair  brush  or  other  implement.  It  is  safer  to 
take  pollen  from  a  flower  that  has  been  kept  covered  with  a 
paper  bag  to  keep  off  foreign  pollen. 

(4)  Cover  the  pollinated  flower  again  with  a  paper  bag 
until  the  fruit  has  grown  considerably. 

392.  General  results  of 
hybridizing.  As  was  men- 
tioned before  (Sect.  390), 
hybrids  are  likely  to  be 
extremely  variable.  Not 
only  may  they  differ  from 
either  parent,  but  they  may 
also  be  unlike  each  other. 
The  differences  include 
such  features  as  the  form, 
size,  quality,  and  other 
characteristics  of  the  entire 
plant  or  of  its  roots,  stems, 
leaves,  flowers,  fruit,  and 
seeds.  Physiological  differ- 
ences, such  as  early  or  late 
maturing,  ability  to  grow 
in  new  conditions  of  soil 
and  climate,  unusual  sus- 
ceptibility to  or  immunity 
from  the  attacks  of  para- 
sitic fungi,  may  appear  and 
are  sometimes  (Sect.  398) 
of  great  economic  impor- 
tance. It  is  much  easier  to 
perpetuate  new  varieties 
unchanged  in  the  case  of  plants  propagated  by  vegetative 
means,  as  by  cuttings  from  roots  or  stems-  or  by  bulbs  or  tubers, 
than  in  the  case  of  those  grown  from  seed.  If  a  desirable 
variety  of  potato  is  obtained  by  hybridizing  and  then  plant- 
ing seeds  from  the  berries  ("potato  balls"),  the  hybrid  can 


FIG.  339.  A  hybrid  wheat  and  the  parent 
forms 

The  hybrid  is  in  the  middle.  It  is  somewhat 
intermediate  between  the  parents,  being 
nearly  (but  not  quite)  beardless  like  the 
right-hand  parent,  with  a  length  of  head 
intermediate  between  the  two  and  with  the 
grains  and  their  covering  bracts  stout,  as 
in  the  left-hand  parent.  Photograph  by 
Minnesota  Agricultural  Experiment  Station 


PLANT  BREEDING 


429 


be  perpetuated  with  certainty  by  planting  tubers  of  the  new 
variety.  But  if  a  hybrid  bean,  pea,  or  wheat  plant  is  produced, 
only  a  few  of  its  seeds  will "  come  true  to  seed  " ;  that  is,  the 
offspring  of  the  hybrid  seeds  will,  many  of  them,  be  what 
breeders  call  "  rogues,"  or  undesirable  varieties,  not  closely 
resembling  their  hybrid  parent.  Year  after  year,  for  several 
generations,  the  garden  plots  containing  descendants  of  the 
new  hybrid  must  be  rogued,  or  gone  over  plant  by  plant, 


FIG.  340.  Variation  in  wheat,  the  hybrid  offspring  of  hybrid  parents 

After  figure  redrawn  from  Transactions  of  the  Highland  and  Agricultural 
Society  of  Scotland 

in  order  to  destroy  all  individuals  but  those  of  the  desired 
variety.  In  the  case  of  wheat,  after  the  fourth  generation  some 
plants  are  usually  to  be  found  that  will  "come  true  to  seed." 
393.  Results  of  hybridizing  the  grains.  In  this  country 
especial  attention  has  been  given  to  hybridizing  Indian  corn 
and  wheat.  Some  valuable  varieties  of  corn  have  already 
thus  been  obtained,  and  many  more  seem  likely  to  be  secured. 
Hybrid  wheats  are  of  importance  for  use  -as  stocks  from  which 
to  breed  and  select.  At  the  agricultural  experiment  stations 
of  the  great  wheat-growing  states  much  time  is  now  spent  in 
hybridizing  wheats  for  breeding  purposes. 


430  PRACTICAL  BOTANY 

394.  Results  of  hybridizing  small  fruits.  The  most  familiar 
hybrids  among  small  fruits  are  grapes.  It  is  probable  that  the 
Delaware  and  the  Catawba  are  hybrids,  and  the  Salem,  Brigh- 
ton, and  Diamond  certainly  are.  Many  varieties  are  directly  or 
remotely  descended  from  hybrids  between  the  European  wine 
grape  and  our  northern  fox  grape,  two  wholly  distinct  species. 


d 

FIG.  341.  Hybrid  plums 

a,  a  stoneless  wild  plum  ;  b,  c,  d,  fruit  of  hybrids  of  a  with  the  French  prune  plum 
All  drawn  to  the  same  scale 

A  favorite  blackberry,  the  Wilson  Early,  is  a  hybrid  between 
two  common  wild  species,  the  high  blackberry1  and  the  dew- 
berry.2 Among  the  descendants  of  hybrids  between  an  almost 
inedible  species3  from  Siberia  and  an  edible  one4  from  Cali- 
fornia is  a  new  constant  species  (not  a  variety),  the  Primus 
blackberry. 

Hybrid  plums  in  the  greatest  variety  have  been  produced 
by  plant  breeders,  especially  by  the  well-known  grower  of 
horticultural  novelties,  Luther  Burbank.  The  amount  of  vari- 
ation in  the  offspring  of  a  single  hybrid  is  suggested  by 
Fig.  341.  One  fruit  of  great  value,  the  Climax  plum,  was 
bred  by  Burbank  as  a  hybrid  between  a  bitter,  tomato-shaped 
Chinese  plum  and  a  Japanese  plum. 

395.  Results  of  hybridizing  citrous  fruits.  Most  valuable 
and  interesting  work  in  hybridizing  plants  of  the  Orange  fam- 
ily has  been  done  by  the  United  States  Department  of  Agri- 
culture, under  the  direction  of  Dr.  H.  J.  Webber.5  The  hardy 

1  Eubus  allegheniensis.  8  R.  cratcegifolius. 

2  R.  villosus.  4  R.  mtifolius. 

6  See  Yearbook  of  the  Department  of  Agriculture,  1904. 


PLANT  BREEDING  431 

trifoliate  orange,  which  resists  our  winters  as  far  north  as  Phila- 
delphia, but  bears  a  small,  bitter,  worthless  fruit,  was  hybridized 
with  the  common  sweet  orange.  Three  valuable  hardy  hybrids 
known  as  citranges  were  produced.  One  of  them  makes  a  good 
substitute  for  grape  fruit,  another  for  lemons,  and  the  third  for 
rather  sour  oranges.  They  may  be  grown  from  two  hundred 
to  four  hundred  miles  farther  north  than  ordinary  oranges. 

Another  citrous  hybrid  is  that  between  the  tangerine  and 
the  grapefruit.  This  is  called  the  tangelo,  and  has  character- 
istics somewhat  intermediate  between  those  of  the  parent  spe- 
cies. It  is  smaller  in  size,  and  the  pulp  is  less  bitter  and  acid 
than  that  of  the  grapefruit,  while  the  "  kid-glove  "  skin,  readily 
peeled  off  with  the  fingers,  is  like  that  of  the  tangerine. 

Our  most  valuable  citrous  fruit  is  the  Washington  navel 
orange,  nearly  or  quite  seedless.  It  originated  from  chance 
seedlings  found  in  a  swamp  along  the  Amazon  and  brought 
from  Bahia,  Brazil,  to  the  United  States  Department  of  Agri- 
culture in  the  early  seventies.  This  orange  forms  by  far  the 
greater  portion  of  the  entire  California  crop  of  over  10,000,- 
000  boxes  a  year. 

396.  Results  of  hybridizing  ornamental  flowers.    Some  of 
the  most  showy  flowers  of  our  gardens  and  greenhouses  are 
hybrids.    Among  the  most  important  examples  are  the  gen- 
era Canna,  Amaryllis,  and  G-ladiolus.    Orchids,  too,  have  been 
hybridized   to   such  an   extent   that  a  dictionary   of  hybrid 
orchids  has  been  prepared. 

In  most  cases  of  flowers  which  have  been  bred  and  hybrid- 
ized for  many  years,  the  process  of  improvement  has  been  due 
partly  to  crossing  and  partly  to  selection.  It  is  often  impos- 
sible to  find  out  how  many  parent  species  or  varieties  have 
entered  into  the  production  of  the  final  hybrid. 

397.  Summary  of  methods  and  results.    Successful  plant 
breeding  requires  a  continuous   effort  to  get  better  plants, 
either  by  picking  out  and  growing  chance  varieties,  or  by  con- 
tinued selection,  first  of  a  set  of  choice  parent  plants,  then 
of  their  best  offspring,  and  so  on  for  several  generations. 


432  PRACTICAL  BOTANY 

Hybridizing  sometimes  (but  not  nearly  always)  aids  the 
plant  breeder  by  giving  him  a  large  number  of  marked 
variations  from  which  to  select. 

High  cultivation,  together  with  plant  breeding,  has  brought 
about  many  astonishing  results.  Plums  three  inches  long  have 
recently  been  produced.  A  hybrid  beach  plum  bears  so  abun- 
dantly that  the  twigs  are  entirely  hidden  by  the  fruit.  The 
largest  cultivated  apples  are  many  hundred  times  the  bulk 
of  their  remote  wild  ancestors.  A  new  variety  of  blackberry 
plant  covers  one  hundred  and  fifty  square  feet  of  soil  and 
bears  a  bushel  or  more  of  fruit.1  Most  cultivated  roots  and 
tubers  have  been  greatly  changed  from  their  wild  condition, 
losing  in  the  proportion  of  woody  fiber  which  they  contain, 
and  gaining  immensely  in  size. 

398.  Securing  varieties  immune  to  disease.  One  of  the  most 
important  problems  for  the  plant  breeder  is  how  to  secure 
varieties  immune  to  diseases.  Two  of  the  most  notable 
achievements  of  our  Department  of  Agriculture  in  this  direc- 
tion have  been  the  production  of  a  disease-resisting  variety 
of  sea-island  cotton  and  of  watermelon.  The  soil  of  valuable 
cotton  plantations  had  come  to  harbor  a  fungus  (Fusarium) 
which  attacked  the  roots  of  the  plants,  plugged  the  vessels 
with  its  hyphse,  and  destroyed  almost  the  entire  crop.  In 
consequence  of  this  many  planters  gave  up  cotton  growing. 
Observation  showed  that  often  in  a  field  where  nearly  all 
the  plants  were  killed,  here  and  there  an  individual  survived, 
blossomed,  and  ripened  its  capsules.  For  four  years  plants 
were  bred  from  the  seeds  of  these  resistant  individuals  until 
a  variety  was  secured  which  withstood  the  attacks  of  the 
fungus  and  made  it  possible  to  resume  cotton  growing  on  the 
abandoned  plantations. 

Extensive  areas  in  the  South,  once  devoted  to  the  culture 
of  watermelons,  became  so  infected  with  a  fungus  that  melon 
growing  was  no  longer  possible.  The  destruction  was  so 

1  See  the  article  by  D.  S.  Jordan,  ff  Some  Experiments  of  Luther  Bur- 
bank,"  Popular  Science  Monthly,  January,  1905. 


PLANT  BREEDING  433 

complete  that  no  process  of  selection  could  be  adopted,  as  in 
the  case  of  the  cotton.  It  was,  however,  found  that  the  roots  of 
the  so-called  "citron,"  a  plant  of  the  watermelon  genus,  were 
not  attacked  by  the  fungus.  Watermelons  were  hybridized 
with  "citrons,"  and  about  a  thousand  varieties  were  grown 
from  the  seeds  thus  obtained.  Many  of  these  proved  resistant, 
but  only  one  was  found  to  be  resistant  and  at  the  same  time 
desirable  in  most  other  respects.  This  one  variety  is  now 
grown  with  good  success  even  on  fungus-infected  soils.1 

COLLATERAL  READING 

The  terms  " Yearbook,"  "Farmers'  Bulletin"  "Bulletin  .  .  .  Bureau  of 
Plant  Industry,"  all  refer  to  the  .publications  of  the  United  States 
Department  of  Agriculture. 

A  very  detailed  list  of  books  and  articles  on  plant  breeding  will  be 
found  in  Bailey,  Plant  Breeding.  The  Macmillan  Company,  New  York. 
Other  titles  not  already  referred  to  in  this  chapter  are  as  follows : 

GENERAL 

Yearbook,  1898,  "  The  Improvement  of  Plants  by  Selection." 
Yearbook,  1906,  "  The  Art  of  Seed  Selection  and  Breeding." 
Farmers'  Bulletin  334,  "  Plant  Breeding  on  the  Farm." 
Bulletin  167,  "New  Methods   of   Plant  Breeding,"  Bureau  of    Plant 

Industry. 
Cyclopaedia  of  American  Horticulture,  article  "Plant  Breeding."   The 

Macmillan  Company,  New  York. 
Cyclopaedia  of  American  Agriculture,  article  "Plant  Breeding."   The 

Macmillan  Company,  New  York. 
The  Principles  of  Breeding,  Davenport.   Ginn  and  Company,  Boston. 

SPECIAL 

Farmers'  Bulletin  229,  "  Production  of  Good  Seed  Corn."  . 
Yearbook,  1906,  "  Corn-Breeding  Work  at  the  Experiment  Stations." 
Yearbook,  1902,  "  Improvement  of  Cotton  by  Seed  Selection." 
Farmers'  Bulletin  342,  "  Potato  Breeding." 

1  See  an  address  by  Dr.  Erwin  F.  Smith  on  "  Plant  Breeding  in  the 
United  States  Department  of  Agriculture,"  before  the  Royal  Horticultural 
Society's  conference  on  genetics. 


CHAPTER  XXIV 
FURTHER  DISCUSSION  OF  PLANT  INDUSTRIES 

399.  Introductory.    Agricultural   and  horticultural  indus- 
tries are  fundamental,  since  they  produce  most  of  the  things 
upon  which  people  live.   A  scientific  study  of  what  plants  are 
and  how  they  live  has  been  the  means  of  raising  these  indus- 
tries to  their  present  high  efficiency.  In  preceding  and  in  later 
chapters  there  is  frequent  reference  to  the  practical  nature  of 
a  knowledge  of  the  principles  of  botany,  but  in  the  present 
chapter  there  are  presented  three  topics  which  relate  specifi- 
cally to  agriculture  and   horticulture.    The  topics  presented 
are:  I.  The  Soil  and  the  Plant;  II.  Special  Care  of  Plants; 
III.  Leading  Agricultural  and  Horticultural  Plants. 

I.    THE   SOIL  AND  THE   PLANT 

400.  Composition  of  the  soil :    rock  material.    One  of  the 
most  important  lines  of  botanical  study  has  to  do  with  the 
interrelations  of  plants  and  the  soil  in  which  they  live.    Any 
extended  consideration  of  agricultural  and  horticultural  indus- 
tries must  involve  a  comprehensive  study  of  the  soils,  but  in 
the  present  connection  only  an  outline  of  the  subject  is  given. 

In  a  general  way  it  may  be  said  that  the  basis  of  soils 
consists  of  more  or  less  finely  divided  rock.  A  study  of  the 
dumping  ground  of  a  stone  quarry  will  show  that  weathering 
processes  are  bringing  about  the  disorganization  of  some  of 
the  stones,  and  as  a  result  soil  is  made  possible.  Sometimes 
water  freezes  and  expands  within  the  crevices  of  the  stone  ;  or 
roots  of  trees  and  other  plants  may  grow  in  these  crevices,  and 
by  expanding  may  break  the  stone.  Organic  material  from 
plants  and  animals  may  help  in  disorganization, -and  landslides 

434 


DISCUSSION  OF  PLANT  INDUSTRIES  435 

may  crush  the  stones,  or  streams  of  water  may  wear  them  into 
smaller  pieces.  In  ancient  times  great  glaciers  crushed  and  wore 
the  stones,  reducing  enormous  masses  to  smaller  ones,  gravel, 
and  finely  pulverized  material.  All  these  agencies  and  others 
have  reduced  the  rocks  so  that  in  soils  we  are  sometimes  unable 
to  find  sand  particles  except  by  means  of  the  microscope. 


EIG.  342.  Production  of  humus  in  the  soil 

A  partially  reclaimed  swamp  in  which  dead  plant  material  several  inches  deep  is 
decaying.  In  the  foreground  is  a  cluster  of  young  skunk-cabbage  leaves,  and  just 
back  of  these  and  in  front  of  the  tree  is  a  cluster  of  unfolding  leaves  of  Clayton's  fern 

In  a  gravelly  soil  there  are  present  small  pebbles  which 
usually  show  by  their  form  and  sometimes  by  their  markings 
the  kind  of  treatment  they  have  undergone.  In  sandy  soil  the 
reduction  of  the  rock  is  more  uniform  and  has  gone  further. 
In  clayey  soil  the  particles  are  so  small  and  fit  together  so 
compactly  that  the  rock  origin  is  not  very  evident.  Peaty  soil 
contains  comparatively  little  rock  material  but  much  more  of 
the  results  of  partial  decay  of  plant  and  animal  bodies.  There 
are  all  possible  gradations  between  these  different  kinds  of  soils. 


436  PRACTICAL  BOTANY 

401.  Composition  of  soils:  organic  matter.    A  brief  study 
of  soils  under  the  microscope  would  show  that  in  addition 
to  rock  in  different  stages  of  decomposition,  there  is  usually 
present  considerable  other  material.    Leaves,  twigs,  wood,  her- 
baceous plants,  and  the  bodies  of  animals  decompose,  and  the 
products  make  up  a  most  important  part  of  the  soil  (Fig.  342). 
In  almost  all  soils  some  organic  matter  may  be  found.   When 
a  large  quantity  of  plant  material  lies  upon  the  surface  of 
the  earth  and  partially  decomposes,  it  is  usually  spoken  of  as 
humus.    In  undrained  or  poorly  drained  swamps  into  which 
little  soil  washes  from  adjacent  hills,  the  deposit  at  the  bottom 
of  the  standing  water  is  almost  pure  organic  matter,  which  is 
the  peaty  material  often  found  in  regions  which  once  were 
swampy. 

402.  Composition  of  the  soil :  water  and  air.   Around  and 
between  the  particles  of  the  more  or  less  decomposed  rock, 
and  absorbed  by  organic  matter,  there  is  always  some  water, 
though  it  may  be  present  in  amounts  so  small  as  to  be  difficult 
of  detection.    Some  water  adheres  closely  about  solid  particles 
of  the  soil.    Water  also  may  fill  the  spaces  between  the  par- 
ticles of  solid  material,  and  such  water  is  known  as  the  free 
water  of  the  soil.   Water  may  take  into  solution  some  portions 
of  the  soil. 

The  amount  of  water  in  the  soil  varies  largely  and  depends 
upon  many  factors.  If  there  is  little  rainfall  and  the  supply 
is  not  replenished  from  below,  the  coarse  soils  (gravel  and 
coarse  sand)  will  soonest  become  dry.  But  the  amount  and 
nature  of  the  organic  matter  in  the  soil  has  much  to  do  with 
ability  to  hold  water.  A  good  supply  is  usually  held  by  fine 
sandy  and  clayey  soils  in  which  there  is  an  abundance  of 
organic  matter.  At  times  of  continued  heavy  rainfall  all  kinds 
of  soil  may  become  filled  with  water,  and  the  prevention  of 
dangers  from  this  surplus  is  discussed  in  the  later  sections  of 
this  chapter. 

In  the  spaces  between  the  solid  particles  of  the  soil  air  is 
also  found.  Even  in  soils  that  are  below  ponds  and  streams 


DISCUSSION  OF  PLANT  INDUSTRIES          437 

there  is  some  air,  though  its  amount  is  usually  so  small  that 
only  water-enduring  plants  can  grow  therein.  Observation  of 
any  porous  soil  immediately  after  a  heavy  rainfall  will  enable 
one  to  see  bubbles  of  air  emerging  from  the  soil  as  the  spaces 
which  they  have  occupied  begin  to  be  filled  by  the  water.  After 
prolonged  rains  most  of  the  air  of  the  soil  may  have  been  ex- 
pelled, and  it  is  generally  supposed  that  in  such  cases  it  is  the 
absence  of  air  as  much  as  the  overabundance  of  water  that 
brings  injurious  results  to  suddenly  submerged  plants.  Obvi- 
ously the  quantities  of  water  and  air  in  the  soil  are  factors 
that  are  constantly  varying  in  amount.  As  a  given  soil  becomes 
dry  it  may  also  become  compact,  and  it  by  no  means  fol- 
lows that  the  total  space  occupied  by  water  and  air  together 
remains  constant. 

403.  Composition  of  the  soil:  living  things  within  it.   A 
highly  important  factor  of  the  soil  consists  of  the  many  kinds 
of  living  things  that  inhabit  it.  Microscopic  plants  and  animals 
of  many  kinds  and  in  great  numbers  live  upon  one  another, 
upon  plant  roots,  or  upon  dead  organic  matter,  and  as  they 
do  so  are  constantly  affecting  the  composition  of  the  soil. 
Then  the  roots  of  living  plants,  the  molds,  and  the  burrow- 
ing animals  such  as  the  larvse  of  insects  and  the  earthworm, 
constantly  take  from,  add  to,  or  otherwise  change  the  soil. 
Earthworms  eat  their  way  through  the  soil,  and  as  they  do 
so  they  make  it  more  porous  and  excrete  materials  that  add 
to  its  available  organic  matter.    Certain  groups  of  soil  bacteria 
have  already  been  discussed  (Sect.  343).    The  living  things 
of  the  soil  may  be  said  to  constitute  an  extensive  and  intricate 
society  of  plants  and  animals  living  close  together  and  greatly 
affecting  the  nature  of  the  material  in  which  they  live. 

404.  Drainage.  The  annual  rainfall  in  different  parts  of  the 
United  States  varies  from  ten  inches  or  less  to  more  than  sixty 
inches  per  year  (Fig.  381).    In  some  parts  of  the  country  the 
total  annual  rainfall  occurs  within  a  short  period,  while  in 
other  regions  it  is  usually  fairly  well  distributed  throughout 
the  year.    In  all  regions  shortage  of  water  is  often  a  source 


438  PRACTICAL  BOTANY 

of  danger  to  plants,  and  surplus  water  may  also  be  injurious, 
Some  of  this  surplus  water  may  run  off  the  surface  without 
ever  entering  the  soil  (Sect.  408).  If  much  of  it  enters  the 
soil  and  remains  for  a  long  time  as  free  water,  it  may  drown 
the  roots  of  plants.  Sometimes  the  slope  of  the  land  surface 
is  such  that  the  free  water  of  the  soil  runs  off  with  sufficient 
rapidity  to  prevent  drowning  of  plant  roots,  but  in  most  cases 
growth  of  plants  is  enhanced  by  artificial  methods  of  under- 
ground drainage.  Ditches  are  made  and  earthen  tile  placed 
in  them,  thus  forming  drainage  courses  which  hasten  the  nat- 
ural underground  flow  of  the  water.  The  cereals  ordinarily 
thrive  best  in  soils  which  contain  from  50  to  60  per  cent  of 
their  total  water-holding  capacity. 

In  swampy  places  artificial  drainage,  which  furthers  the 
growth  of  economic  plants,  also  restrains  the  growth  of  those 
swamp  plants  which  ordinarily  thrive  in  wet  soils.  Much  of 
our  best  land  has  been  made  available  by  drainage,  and  there 
are  enormous  areas  that  would  be  most  valuable  if  only  they 
were  properly  drained.  It  has  been  estimated  by  Professor 
Shaler  that  along  the  Atlantic  coast  alone  there  are  over 
3,000,000  acres  of  swamp  lands  that  it  is  possible  to  reclaim 
by  drainage.  The  estimates  of  the  United  States  government 
indicate  that  in  our  country  there  are  nearly  100,000,000  acres 
of  swamp  land.  There  are  thirty-five  states  in  the  eastern  half 
of  the  United  States  in  which  there  are  over  30,000,000  acres 
of  swamp  lands.  Much  of  this  vast  area  can  be  drained,  and 
may  then  become  the  growing  place  for  valuable  economic 
plants  instead  of  the  relatively  valueless  swamp  plants. 

When  underground  drainage  for  ordinary  cultivated  fields 
was  first  advocated,  opponents  asserted  that  while  it  might  be 
helpful  in  removing  surplus  water  during  times  of  abundant 
rain,  the  same  drains  would  be  the  means  of  depletion  of  the 
water  during  times  of  drought.  Practice  has  shown,  however, 
that  if  surplus  water  is  removed  in  rainy  seasons,  plant  roots 
grow  deeper  into  the  soil  and  are  thereby  better  placed  for 
enduring  subsequent  dry  periods.  Furthermore,  the  thin  films 


DISCUSSION  OF  PLANT  INDUSTRIES  439 

of  water  which  adhere  to  soil  particles  are  not  removed  by 
drainage,  and  plant  roots  are  better  located  to  avail  themselves 
of  this  supply  than  if  they  are  placed  near  the  surface,  as 
happens  in  wet  soils. 

Within  the  last  decade  it  has  been  shown  that  at  least  some 
of  the  cereals  secrete  and  leave  within  the  soil  substances 
which  are  injurious  to  the  kinds  of  plants  which  produce 
them.1  Adequate  drainage  probably  assists  in  removing  some 
of  these  poisonous  materials.  Drainage  ditches  help  to  aerate 
the  soil,  and  in  this  way  are  of  great  benefit  to  the  growth  of 
economic  plants. 

405.  Tillage  and  water  supply.  In  olden  times  agriculturists 
advised  against  cultivating  corn  and  other  crops  during  times 
of  drought,  because  they  thought  that  if  constantly  stirred  the 
soil  would  lose  its  moisture  more  rapidly.  People  now  know 
that  it  is  of  the  greatest  importance  to  till  the  soil  during 
droughts  in  order  that  it  may  not  lose  its  moisture.  An  illus- 
tration will  help  in  studying  this  matter.  If  two  pieces  of  loaf 
sugar  are  placed  one  upon  the  other,  the  lower  one  held  in 
the  thumb  and  finger  and  the  other  left  lying  loosely  upon 
the  first  and  not  touching  the  fingers  at  all,  and  if  the  lower 
one  is  then  placed  in  contact  with  water,  two  important  facts 
are  shown.  The  lower  piece  takes  up  water  freely,  but  the 
upper  one,  though  lying  upon  the  lower  wet  piece,  becomes 
wet  only  after  a  long  time.  Close  connection  between  the 
solid  particles  is  necessary  for  the  rapid  upward  passage  of 
the  water. 

When  soils  are  compact,  moisture  from  the  deeper  portions 
passes  upward  freely,  as  in  the  lower  lump  of  sugar,  and  evap- 
orates into  the  air.  If,  however,  the  surface  is  kept  loose  and 
finely  pulverized,  so  that  the  particles  are  less  closely  conr 
nected,  moisture  does  not  readily  pass  through  it  and  there 
is  less  loss  from  evaporation.  The  roots  of  plants  being  more 

1  Schreiner,  0.,  and  Reed,  H.  S.,  Some  Factors  influencing  Soil  Fertility. 
"Bur.  Soils,"  Bulletin  40,  U.  S.  Dept.  Agr.,  1907.  Also,,  "  The  Production  of 
Deleterious  Excretions  by  Roots,"  Bulletin  34,  Torrey  Bot.  Club,  1907. 


440  PRACTICAL  BOTANY    . 

deeply  placed,  are  in  contact  with  the  moist  soil  from  which 
a  supply  of  water  may  be  secured.  The  depth  to  which  roots 
are  known  to  go  in  regions  where  the  water  is  found  only  at 
great  depths  is  discussed  in  Sect.  27. 

For  a  long  time  it  was  supposed  that  the  chief  reason  for 
cultivating  plants  was  to  keep  down  the  weeds,  but  we  here 
see  that  this  is  but  a  small  part  of  the  truth.  Weeds  have 
been  of  much  advantage  to  agriculture,  since  in  keeping  them 
down  the  farmer  has  tilled  the  soil  so  as  to  help  regulate  the 
moisture  supply  for  the  growing  plants. 

406.  Dry-land  farming.    It  has  been  shown  that  the  culti- 
vable area  of  the  earth  may  be  extended  by  drainage  of  un- 
used swamp  areas ;  but  it  may  be  greatly  extended  if  water  in 
proper  quantity  and  at  the  proper  times  is  placed  upon  arid 
lands.    It  is  said  that  approximately  two  fifths  of  the  area  of 
the  United  States  is  too  dry  for  cultivation  without  irrigation. 

Dry-land  farming  is  one  method  now  being  tried  in  regions 
where  there  is  some  rainfall,  but  an  amount  that  is  insufficient 
to  produce  a  good  crop.  By  careful  tillage  of  the  soil  the 
scanty  rainfall  is  conserved,  and  in  this  way  most  of  the  rain- 
fall of  two  or  more  years  may  be  used  for  one  crop.  Good 
crops  have  been  grown  in  this  way,  but  it  is  evident  that 
much  work  over  a  long  period  is  necessary  in  order  to  accu- 
mulate enough  water  for  one  crop.  It  is  hoped  that  drought- 
enduring  and  drought-resisting  varieties  of  economic  plants, 
especially  wheat  and  other  cereals,  may  be  found  or  devel- 
oped, thus  increasing  the  outlook  for  dry-land  farming. 

407.  Irrigation.  The  practice  of  irrigating  lands  is  in  some 
parts  of  the  earth  a  very  old  one.    Its  extensive  use  in  the 
United  States  is  recent  and  both  the  government  and  private 
enterprises  have  expended  enormous  sums  of  money  in  sup- 
plying water  from  lakes  and  rivers  to  lands  which  previously 
were  non-productive.  In  some  cases  this  has  involved  damming 
the  mountain  streams  and  diverting  the  water  over,  around, 
or  through  mountains,  and  finally  to  the  valleys  to  be  culti- 
vated.  With  control  of  the  water  supply,  fertile  soil,  abundant 


DISCUSSION  OF  PLANT  INDUSTEJES  441 

sunshine,  and  freedom  from  sudden  changes  in  climate,  it 
is  evident  that  there  is  a  great  future  for  irrigated  lands. 
Already  over  13,000,000  acres  are  under  irrigation,  and  other 
projects  that  are  now  under  way  will  add  largely  to  that 
amount.  Even  with  this  large  acreage  added  to  our  tillable 
soil,  it  must  be  kept  in  mind  that  only  a  very  small  portion 
of  the  arid  lands  has  been  or  apparently  can  be  supplied  with 
water  from  the  sources  that  are  now  available. 

408.  Removal  of  soil  by  winds  and  water.  Currents  of  air 
constantly  carry  particles  of  dust.  During  periods  when  the 
earth's  surface  is  dry  the  amount  of  dust  thus  carried  is  large. 
If  a  pane  of  glass  that  has  been  moistened  with  oil  is  exposed 
for  a  time  to  the  wind  on  a  dry  day,  and  then  examined  with 
a  strong  magnifying  glass,  it  will  furnish  a  good  demonstra- 
tion of  the  dust-carrying  power  of  moving  air.  Further  illus- 
trations are  found  in  the  dust  that  strikes  our  faces  on  windy 
days,  and  in  that  which  is  deposited  on  window  sills.  Win- 
dow panes  in  the  houses  near  the  end  of  Cape  Cod  finally 
become  translucent,  like  ground  glass,  from  the  action  of  sand 
driven  by  the  wind.  When  cultivated  fields  become  dry  the 
wind  may  carry  away  large  quantities  of  soil.  This  is  some- 
times well  shown  in  winter  when  snow  covers  the  ground  in 
such  protected  places  as  the  leeward  slopes  of  hills.  Soil  which 
has  been  frozen  dry  is  often  carried  from  other  regions  by  the 
wind  and  dropped  upon  these  leeward  snow  banks  in  such 
quantities  as  to  bury  the  snow  completely.  Good  windbreaks 
about  cultivated  fields  help  to  prevent  loss  of  soils  by  wind. 

Rapidly  running  surface  water  often  carries  away  part  or 
all  of  the  fertile  soil.  In  grasslands,  meadows,  and  forested 
areas,  surface  water  is  retarded  in  its  rate  of  flow,  and  conse- 
quently does  not  carry  away  much  soil.  In  regions  that  were 
once  forested  and  from  which  the  timber  has  now  been  largely 
removed,  the  surface  water  soon  erodes  ditches  (Fig.  343), 
which,  with  rapidly  deepening  channels  and  developing  tribu- 
taries, will  in  a  few  years  carry  away  much  of  the  fertile  soil 
of  the  forest  floor.  After  forest  fires,  which  themselves  destroy 


442 


PRACTICAL  BOTANY 


much  of  the  humus  of  the  forest  soils  (Fig.  344),  the  surface 
water,  which  is  no  longer  retarded  and  absorbed  by  humus, 
flows  with  increased  rapidity.  In  so  doing  it  carries  away  large 
quantities  of  soil,  sometimes  uncovering  the  burned  roots  until 
the  trees  are  easily  overturned  by  winds.  An  area  once  for- 
ested may  soon  be  cut  into  trenches  and  ridges  until  the  only 


FIG.  343.  Erosion  of  the  soil  following  removal  of  the  forest 

This  land  was  covered  with  a  heavy  pine  forest,  and  had  a  good  soil,  which  was 

held  upon  the  forest  floor.   When  the  timber  was  removed,  erosion  soon  cut 

ditches  through  the  pasture  land 

remaining  evidence,  if  any,  of  its  previously  forested  condition 
is  seen  in  the  presence  of  a  few  plants  such  as  young  trees 
that  are  trying  to  grow  in  the  poor  soil  that  is  left  (Fig.  346). 
There  are  several  means  of  preventing  much  of  this  loss  of 
soil  by  erosion.  In  wooded  regions  judiciously  cutting  part  of 
the  timber  each  year  rather  than  cutting  all  of  it  at  once  gives 
opportunity  for  new  plants  to  occupy  and  hold  the  soil.  There 


FIG.  344.  Humus  of  the  soil,  and  roots  of  red  spruce  and  balsam  fir  burned 
by  forest  fire.  Photograph  by  United  States  Forest  Service 


443 


444  PRACTICAL  BOTANY 

are  many  kinds  of  soil-holding  plants  which,  if  properly  placed, 
will  prevent  erosion  in  its  earliest  stages,  and  these  should  be 
used.  In  open, 'hilly  fields  which  are  exposed  to  erosion,  grass 
and  meadow  crops  are  desirable,  since  their  roots  help  to  hold 
the  soil  throughout  the  whole  year.  In  such  cases  the  roots 
and  stems  help  to  prevent  the  rapid  run-off  of  the  surface 
water.  The  very  things  that  need  to  be  done  in  the  cultiva- 
tion of  plants  increase  the  danger  of  loss  of  soil  where  rapid 
flow  of  the  surface  water  cannot  be  prevented.  In  hilly  fields 


FIG.  345.  A  Mississippi  hillside  farm,  newly  cleared 

It  is  plowed  and  planted  in  rows  around  the  hill  to  retard  erosion.  In  such  regions 
the  soil  when  plowed  washes  away  rapidly.  Photograph  furnished  by  W.  N.  Logan 

it  is  often  difficult,  sometimes  impossible,  to  prevent  erosion. 
In  some  localities  the  rows  of  growing  plants  are  arranged 
across  the  slope  of  the  hill  (Fig.  345),  thus  assisting  some- 
what in  retarding  the  surface  flow  of  water.  If  cultivation  is 
continued  in  such  places,  the  soil  soon  erodes,  and  it  is  with 
extreme  difficulty  that  any  plants  gain  a  foothold  (Fig.  346). 
In  some  foreign  countries  hillsides  have  been  saved  for  cultiva- 
tion by  a  process  of  terracing.  The  terraces  are  constructed  in 
such  a  way  that  the  soil  upon  each  is  level  or  slopes  toward 
the  hill,  thus  retarding  or  preventing  erosion  (Fig.  347). 


446 


446 


PRACTICAL  BOTANY 


Terraced  farms  sometimes  are  desirable  for  vineyards,  but  it 
is  obvious  that  for  ordinary  crops  such  elaborate  care  will 
prove  profitable  only  where  available  land  is  extremely  scarce. 


FIG.  347.  Landward  slope  of  an  Italian  promontory,  the  loose,  loamy  soil 

terraced  to  prevent  erosion  when  under  cultivation  as  a  vineyard 

Modified  from  a  photograph 

111  localities  with  moderate  slope  of  the  surface,  underground 
drains  may  prevent  erosion  except  at  times  of  extremely  heavy 
rains.  Many  ditches  that  were  formerly  supposed  to  be  too 
large  to  be  taken  underground  have  been  so  placed  with  great 
advantage. 


DISCUSSION  OF  PLANT  INDUSTEIES 


447 


409.  Soils  and  plant  nutrition.  Soils  differ  widely  in  their 
ability  to  support  vegetation.  Even  the  roots  from  one  plant 
may  develop  quite  differently  in  different  soils,  as  is  shown 
when  the  roots  are  arranged  so  that  part  of  them  grow  in 
clean  sand  and  part  in  rich  loam  (Fig.  348).  A  comparison 
of  plants  of  the  same  kind  that  have  been  grown  in  regions 
that  have  different  kinds  of  soil  will  show  wide  differences. 
From  the  point  of  view  of  the  growth  of  our  economic  plants, 


FIG.  348.  Effect  of  quality  of  soil  on  growth  of  roots 

The  cucumber  plant  shown  in  the  figure  was  grown  in  a  shallow  box,  one  end  of 
which  was  filled  with  sand  and  the  other  with  rich  loam.  The  seed  was  planted 
in  the  sand,  quite  near  the  partition  (p)  of  mosquito  netting,  which  separated  the 
sand  from  the  loam.  When  the  plant  was  one  foot  high  the  earth  and  sand  were 
washed  away  and  the  roots  sketched.  Those  grown  in  the  loam  weighed  nine 
times  as  much  as  those  in  the  sand.  Three  eighths  natural  size 

that  soil  is  best  which  with  the  proper  amount  of  cultivation 
will  produce  the  best  and  largest  yield  of  plant  material.  Such 
a  soil  is  said  to  be  fertile. 

There  are  now  in  progress  many  experiments  relative  to 
the  nature  of  soil  fertility,  and  many  disputed  questions  are 
involved.  Into  these  difficulties  we  shall  not  enter.  How- 
ever, a  study  of  the  way  in  which  plant  foods  are  built  up 
(Sect.  17),  and  of  the  chemical  analyses  that  have  been  made 
of  plants  and  of  soils,  enables  us  to  know  some  of  the  facts 


448 


PEACTICAL  BOTANY 


concerned.  Carbon  dioxide  comes  from  the  air,  water  from 
the  soil,  and  with  the  water  there  are  carried  into  the  plants 
compounds  of  nitrogen,  potassium,  phosphorus,  magnesium, 
calcium,  iron,  sulphur,  etc.  Uncombined  nitrogen  exists  in  the 
air,  but  as  such  it  is  unavailable  to  green  plants.  In  the  soil, 
when  nitrogen  exists  in  combination  with  oxygen  as  a  nitrate 
(NO3)  green  plants  may  use  it.  The  following  tables  show 
the  amount  of  these  substances  contained  in  the  soil  and  the 
amount  used  in  a  given  quantity  of  plant  product. 

RELATIVE  **  SUPPLY  AND  DEMAND  "  OF  SEVEN  ELEMENTS  l 


SUBSTANCES 

Pounds  in  2,000,000 
pounds  of  the  aver- 
age crust  of  the  earth 

Pounds  in  100 
bushels  of  corn 
(grain  only) 

2  200 

17 

49200 

19 

48  000 

7 

68,800 

u 

88,600 

1 

Sulphur     .    •     .                   •          *    • 

2  200 

1 

4 

Pounds  above  one 
acre  of  ground 

70,000,000 

100 

MINERAL  PLANT  FOOD  IN  WHEAT,  CORN,  OATS,  AND  CLOVER  2 


PRODUCE 

Phos- 
phorus 
(pounds) 

Potas- 
sium 
(pounds) 

Magne- 
sium 
(pounds) 

Calcium 
(pounds) 

Iron 

(pounds) 

Sulphur 
(pounds) 

KIND 

AMOUNT 

Wheat  (grain) 

50    bu. 

12 

13 

4 

1 

.3 

.1 

Wheat  (straw) 

2£  tons 

4 

45 

4 

9.5 

1.5 

2 

Corn  (grain) 

100    bu. 

17 

19 

7 

1.3 

.4 

.2 

Corn  (fodder) 

3    tons 

6 

52 

10 

21 

4.8 

5.8 

Oats  (grain) 

100    bu. 

11 

16 

4 

2 

.5 

.6 

Oats  (straw) 

2£  tons 

5 

52 

7 

15 

2.8 

3 

Clover  (seed) 

4    bu. 

2 

3 

1 

.5 

.1 

Clover  (hay) 

4    tons 

20 

120 

31 

117 

4 

6.4 

1  After  Hopkins,  C.  G.,  Table  8,  Soil  Fertility  and  Permanent  Agricul- 
ture, 1910.  2  Ibid.,  Table  13. 


DISCUSSION  OF  PLANT  INDUSTRIES  449 

410.  The  nitrogen  supply.   The  nitrogen  supply  of  plants 
has  already  received  attention  in  Sect.  343,  Chapter  XXI, 
which  should  be  reviewed  in  the  present  connection.    Long 
before  the  action  of  the  soil  bacteria  was  known,  agricultur- 
ists knew  of  the  value  of  clover  and  other  leguminous  plants 
as  a  means  of  helping  to  maintain  or  regain  the  fertility  of 
the  soil.  It  is  now  known  that  when  soils  are  poor  in  nitrogen 
compounds  it  is  possible  to  replenish  the  nitrates  from  the 
atmospheric  nitrogen  by  the  use  of  clover  and  its  relatives, 
upon  the  roots  of  which  grow  tubercles  containing  the  nitro- 
gen-fixing bacteria.    Sometimes  it  is  difficult  to  get  clover  to 
grow  in  old  and  much-worn  soils.    This  may  be  due  to  the 
fact  that  there  are  no  nitrogen-fixing  bacteria  in  the  soil  to 
start  the  tubercles.    In  such  cases  they  must  be  introduced 
from  a  soil  in  which  they  are  growing,  or  from  artificial  cul- 
tures.   The  best  way  of  introducing  them  consists  in  scatter- 
ing over  the  impoverished  field  some  soil  from  fields  in  which 
tubercle-bearing  plants  have  grown.    Successful  clover  fields 
and  waste  places  in  which  the  common  sweet  clover  (Melilo- 
tus~)  grows,  furnish  good  soil  for  infecting  worn-out  lands. 

Some  much-used  soils  have  become  quite  acid,  and  this 
acidity  seems  to  interfere  with  growth  of  the  tubercle-forming 
bacteria.  It  has  been  found  necessary  in  many  cases  to  coun- 
teract this  acidity  with  limestone  before  the  tubercle  bacte- 
ria can  flourish  upon  the  clover  roots  and  thus  produce  the 
nitrates  that  are  needed  for  nutrition  of  the  clover  and  the 
enrichment  of  the  soil. 

411.  Is  fertility  permanent?   It  is  a  fact  of  common  obser- 
vation that  when  a  given  crop  of  plants  is  cultivated  upon  the 
same  soil  for  a  long  period,  of  years  the  yield  of  the  crop 
diminishes.    Agriculturists  learned  a  very  long  time  ago  that 
by   growing   different  crops  in  rotation  better  yields  were 
secured.  But  even  with  this  rotation  of  crops  and  with  careful 
cultivation,  the  annual  yield  decreases  unless  the  soil  is  replen- 
ished in  some  way.    The  oldest  experiments  of  which  there 
are  complete  records  are  still  in  progress  at  the  Rothamsted 


450  PEACTICAL  BOTANY 

Experimental  Station,  Harpenden,  England.  Some  of  these 
began  in  1848.  Certain  crops  have  there  been  grown  year 
after  year  upon  the  same  soil.  A  barley  field,  which  has 
been  unfertilized  since  the  experiments  began,  produced  in 
the  year  1849  a  little  over  40  bushels  per  acre.  Each  year 
thereafter,  with  no  fertilization,  barley  has' been  grown  on  the 
same  field,  and  the  yield  has  steadily  decreased,  so  that  dur- 
ing the  twenty  years  closing  in  1909  the  average  per  year 
was  less  than  15  bushels  per  acre.  Another  piece  of  ground 
was  used  for  wheat,  turnips,  and  clover,  in  rotation,  with 
three  years  given  to  each  rotation,  and  was  fertilized  by  use  of 
nitrogen  and  mineral  fertilizers.  Considering  only  the  wheat 
records,  we  have  the  following :  In  the  first  twenty  years  the 
average  yield  of  wheat  for  the  years  in  which  wheat  was  grown 
was  35.3  bushels  per  acre ;  in  the  second  period  of  twenty 
years  the  average  yield  was  32  bushels  per  acre ;  and  in  the 
third  period  of  twenty  years  the  average  yield  was  36.4  bushels 
per  acre.  In  the  second  twenty-year  period  one  year  of  general 
wheat  failure  materially  reduced  the  average  for  that  period. 

412.  Soil  improvement.  Since  plants  use  such  large  quantities 
of  the  materials  that  are  named  in  the  tables  given  above,  it  is 
apparent  that  any  soil  to  be  fertile  must  contain  these  materials. 
Merely  containing  them,  however,  does  not  make  a  soil  fertile. 
They  must  be  in  the  particular  combination  in  which  plants 
can  take  them ;  the  soil  must  be  of  such  a  texture  and  physical 
nature  as  to  permit  the  processes  through  which  plants  secure 
their  foods.  Such  chemical  substances  within  the  soil  as  strong 
solutions  of  injurious  salts,  if  present  in  sufficient  quantities, 
will  prevent  the  passage  of  materials  into  the  plant. 

A  fertile  soil,  then,  is  one  that  has  the  following  requisites : 
a  favorable  water  content,  a  good  supply  of  mineral  substances 
necessary  to  plant  growth,  freedom  from  harmful  chemical 
substances,  and  favorable  texture  and  physical  composition. 
Many  soils  that  once  were  fertile  have  become  almost  or  quite 
unproductive,  either  through  exhaustion  of  food  elements,  or 
through  accumulation  of  harmful  substances,  and  vigorous 


DISCUSSION  OF  PLANT  INDUSTRIES  451 

study  is  now  being  made  regarding  the  nature  of  these  limit- 
ing factors.  The  Rothamsted  experiment  and  hundreds  of 
others  that  have  been  made  in  the  United  States  show  the 
good  effects  upon  soil  fertility  that  may  be  secured  by  proper 
rotation  of  crops  and  proper  care  of  the  soil. 

II.   SPECIAL  CARE  OF  PLANTS 

413.  Horticulture  and  gardening.  Scientific  study  has  aided 
much  not  only  in  the  matter  of  the  better  growth  and  care  of 
field  crops  and  the  forests,  but  in  gardening  and  agriculture 
as  well.   All  that  has  been  said  about  what  a  plant  is  and  how 
it  lives,  and  about  soils,  cultivation,  and  plant  food,  applies  in 
some  way  to  gardening  and  agriculture  ;  it  must  be  recognized, 
moreover,  that  each  garden  or  orchard  crop  is  a  specialty  in 
itself,  and  requires  special  study  for  mastery.    Almost  every 
kind  of  garden  or  orchard  plant  thrives  and  yields  best  in  cer- 
tain climates,  in  certain  kinds  of  soils,  often  with  certain  kinds 
of  exposure  to  light;  has  its  own  peculiar  diseases,  and  re- 
quires particular  treatment  in  caring  for  its  matured  product. 
It  can  be  no  part  of  this  general  discussion  of  botany  to  deal 
with  such  matters  in  detail,  but  two  or  three  kinds  of  special 
care  should  be  discussed  as  illustrations  of  the  nature  of  the 
work  that  is  being  done. 

414.  Pruning.  In  Sect.  60,  Chapter  IV,  there  was  a  discus- 
sion of  the  way  in  which  natural  pruning  occurs.    Artificial 
pruning  has  become   a  general  practice,   and  the  botanical 
relations  of  the  process  are  therefore  significant. 

In  injured  plants,  whose  branches  have  been  broken  by  wind 
or  other  destructive  agencies,  cutting  away  the  broken  parts 
discontinues  the  passage  of  food  into  the  injured  portions, 
makes  it  possible  for  new  branches  to  grow  into  the  space 
occupied  by  the  injured  branches,  and  decreases  the  danger  of 
disease  infection.  Often  the  last  result  is  not  secured  because 
the  cut  area  is  not  treated  so  as  to  prevent  entrance  of  fungus 
spores,  bacteria,  or  insect  parasites.  When  the  wound  that  is 


452  PEACTICAL  BOTANY 

made  by  pruning  is  small,  the  cambium  layer  sometimes  grows 
over  the  cut  surface,  the  wound  thus  healing  without  becom- 
ing the  place  of  infection.  But  large  wounds  are  almost  cer- 
tain to  become  infected  with  fungus  spores  before  they  heal, 
and  they  thus  become  the  means  of  injury  or  destruction  of  the 
whole  plant.  A  heavy  coat  of  paint  placed  upon  the  cut  sur- 
face usually  prevents  the  entrance  of  destructive  organisms. 

At  transplanting,  all  injured  roots  are  pruned  away  and  new, 
vigorous  roots  are  soon  developed.  During  the  time  when  the 
roots -are  becoming  established,  transpiration  of  water  from 
the  aerial  parts  may  greatly  endanger  the  plant.  This  is  one 
of  the  reasons  for  heavy  pruning  of  the  top  at  the  time  of 
transplanting.  After  the  top  has  been  pruned  new  growth 
develops,  and  by  the  time  the  root  system  is  established  and 
is  thus  in  position  to  take  up  water,  the  increased  transpiring 
surface  produced  by  the  new  growth  may  be  supplied  with 
water.  When  transplanting  potted  plants  into  the  garden  it 
is  often  necessary  to  cover  or  otherwise  protect  them  against 
excessive  transpiration  until  the  roots  are  established.  This 
serves  the  same  purpose  that  pruning  does  in  transplanting 
woody  plants.  Indeed,  succulent  potted  plants  are  sometimes 
pruned  when  they  are  transplanted. 

Pruning  for  better  form  is  extensively  practiced  in  caring 
for  the  shrubs  and  trees  of  lawns  and  parks.  By  pruning  to 
determine  just  what  part  of  a  plant  may  develop,  almost  any 
desired  form  may  be  produced.  In  this  way  apple  trees  have 
been  made  to  grow  as  vines,  roses  have  been  made  to  grow 
like  box  hedges,  and  grapevines  have  been  made  into  upright 
and  self-supporting  shrubs. 

In  pruning  for  better  flowers  and  fruit,  only  a  comparatively 
small  number  of  vigorous  buds  or  branches  are  permitted  to 
grow.  In  this  way  each  bud  which  grows  receives  proportion- 
ately much  more  nourishment  from  the  whole  plant  than 
would  be  true  if  all  the  parts  had  remained.  If  all  but  one  or 
two  of  the  flower  buds  of  a  tomato  plant  are  pruned  away, 
larger  and  better  fruit  is  produced.  Chrysanthemums  and 


DISCUSSION  OF  PLANT  INDUSTRIES  453 

roses  are  often  treated  in  the  same  way  with  striking  results. 
Many  of  the  large  and  perfect  flowers  and  fruits  that  are  shown 
in  exhibitions  are  developed  in  this  way.  Successful  orchard 
growers  prune  their  trees  moderately  each  year,  and  thus  main- 
tain the  quality  and  quantity  of  woody  branches  from  which  the 
largest  yield  of  good  fruit  may  be  secured  (Fig.  350).  Checking 


FIG.  349.    Photograph  by  the  New  York  Agricultural  Experiment  Station 
illustrating  the  results  of  spraying  potatoes  to  prevent  disease 

Those  that  were  not  sprayed  yielded  at  the  rate  of  161  bushels  per  acre ;  those 
sprayed  three  times  during  the  season  yielded  at  the  rate  of  350£  bushels  per  acre ; 
those  sprayed  every  two  weeks  yielded  at  the  rate  of  380  bushels  per  acre.  In 
other  experiments  the  results  are  even  better.  In  this  same  station,  during  the 
year  1904,  the  average  gain  per  acre  in  the  yield  for  three  sprayings  is  191  bushels, 
and  for  spraying  every  two  weeks  is  233  bushels 

the  vegetative  growth  of  the  plant  at  the  right  time  seems  to 
stimulate  flower  and  fruit  production.  All  kinds  of  orchard 
trees  are  more  productive  when  properly  pruned.  In  recent 
times  pruning  in  order  to  facilitate  proper  spraying  has  become 
a  prominent  feature  of  the  work.  The  various  factors  that  are 
now  involved  in  the  practice  of  pruning  are  of  such  importance 
that  the  subject  has  become  almost  a  specialty  in  itself. 


454 


PRACTICAL  BOTANY 


415.  Checking  and  removing  disease.  The  prevalence  of 
plant  diseases  has  been  made  apparent  in  preceding  chapters. 
Although  the  nature  of  many  of  these  diseases  is  not  known, 
scientific  study  has  contributed  methods  of  prevention,  control, 
or  elimination  in  many  cases.  Oat  smut,  which  on  an  average  is 
said  to  destroy  each  year  from  one  dollar  to  five  dollars'  worth 


FIG.  350.   Results  of  proper  pruning  and  spraying  in  growing  Jonathan 
apples,  Spokane,  Washington 

The  number  and  average  size  of  the  apples  are  increased  and  the  quality  is 
improved.   Photograph  by  August  Wolf 

of  oats  per  acre,  can  be  removed  by  application  to  the  seed  of 
a  formalin  solution  at  a  cost  of  a  few  cents  per  acre.  It  is  not 
uncommon  for  the  yield  of  an  apple  orchard  to  be  doubled  by 
proper  spraying,  and  the  accompanying  improvement  in  the 
quality  of  the  fruit  changes  it  from  a,  poor  quality  with  a  poor 
market,  if  it  has  any  at  all,  to  a  good  quality  with  good  market. 
A  very  carefully  recorded  experiment  in  the  value  of  con- 
trolling the  disease  known  as  potato  blight  illustrates  the 


DISCUSSION  OF  PLANT  INDUSTRIES  455 

possibilities  of  such  treatment  (Fig.  349).  Three  rows  of 
potatoes  were  planted  side  by  side,  the  planting  and  cultiva- 
tion of  all  being  the  same.  The  results  from  different  kinds 
of  spraying,  as  shown  in  the  legend  under  the  figure,  indi- 
cate clearly  the  great  importance  of  this  treatment.  If  you 
will  ascertain  the  price  of  potatoes  in  your  local  market,  and 
estimate  the  value  of  the  increased  yield,  its  significance  will 
be  more  fully  seen.  It  costs  as  much  in  money  and  labor  to 
plant  and  cultivate  a  poor  crop  as  a  good  one. 

416.  An  artificial  association  of  plants.  By  draining  or  irri- 
gating, cultivating  and  fertilizing  the  soil,  planting  the  seed 
or  plants  at  the  right  time  and  in  the  best  way,  caring  for 
them  and  fighting  their  diseases,  a  highly  artificial  and  depend- 
ent association  of  plants  has  been  developed.  None  of  these 
plants  would  naturally  grow  alone  and  unmixed  with  other 
plants.  They  have  been  cultivated  and  protected  until,  when 
this  cultivation  and  protection  are  discontinued,  their  produc- 
tivity rapidly  decreases.  They  would  soon  be  unable  to  hold 
their  own  against  the  many  natural  plants  that  would  begin  to 
occupy  the  previously  cultivated  region.  Many  of  the  charac- 
teristics for  which  cultivated  plants  are  valued,  such  as  tender 
stems  or  foliage,  seedless  fruits,  and  double  flowers,  tend  to 
weaken  their  capacity  to  succeed  in  the  struggle  for  existence. 


III.   LEADING  AGRICULTURAL  AND  HORTICULTURAL 

PLANTS 

417.  Commercial  importance  of  the  cereals.  Under  the  name 
cereals  are  included  many  economic  plants  of  the  Grass  family. 
They  produce  grains  (seeds  or  fruits)  in  which  food  material 
is  stored  in  compact  form.  The  principal  cereals  named  in  the 
order  of  their  yields  for  the  whole  world,  stated  in  tons  of 
2000  pounds,  are: 

Corn      t     .     .     .     .     109,000,000         Rice 53,500,000 

Wheat 103,500,000         Rye 40,500,000 

Oats      .     ....       57,000,000         Barley 31,000,000 


456  PRACTICAL  BOTANY 

In  the  United  States  the  average  annual  value  of  the  grain 
and  hay  crops  for  the  five  years  1903-1907  was  as  follows1: 

Corn      ...    O.  '•'•     .     .     .     .     .$1,132,000,000 

Hay 587,000,000 

Wheat .        503,000,000 

Oats 293,000,000 

Barley 70,000,000 

418.  Indian  corn.  Indian  corn  is  an  American  plant,  well 
known  to  the  Indians  and  cultivated  by  them  long  before  the 
coming  of  white  people.  Its  food  value  per  acre  is  about 
double  that  of  other  grains. 

The  United  States  is  the  chief  corn-raising  country,  pro- 
ducing more  than  three  quarters  of  the  world's  crop,  mainly 
in  the  "  corn  belt "  of  the  Middle  West.  This  region,  with  its 
fertile  soil,  its  sunny  summers,  a  fairly  heavy  rainfall,  and  a 
high  summer  temperature,2  is  especially  adapted  for  corn  grow- 
ing. In  northern  Europe  corn  is  grown  in  botanic  gardens  as 
a  curiosity,  but  does  not  succeed  as  a  field  crop  because  the 
summer  temperature  is  not  high  enough  and  there  is  not  suffi- 
cient sunshine.  In  the  Mediterranean  region  the  soil  is  fertile 
and  the  summers  are  sunny  and  hot,  but  the  scanty  summer 
rainfall  —  sometimes  less  than  an  inch  during  three  months  — 
affords  unfavorable  conditions  for  corn  growing. 

The  most  important  types  of  corn  are  flint  corn,  dent  corn, 
and  sweet  corn.  The  flint  varieties  have  a  large  proportion 
of  hard,  translucent  endosperm.  The  dwarfed,  quickly  matur- 
ing kinds,  which  can  be  harvested  in  ninety  days  or  less  from 
the  time  of  planting,  and  which  are  therefore  grown  in  the 
northernmost  states  and  Canada,  are  all  flint  varieties.  The 
dent  varieties  have  much  soft  endosperm  and  indented  kernels 
(Fig.  332).  The  plants  sometimes  reach  a  height  of  eighteen 
feet  or  more,  and  require  nearly  six  months  to  mature.  Dent 
corn  is  much  more  productive,  as  a  rule,  than  the  flint  varieties, 

1  See  Yearbook,  U.  S.  Dept.  Agr.,  1907. 

2  Averaging  between  70°  and  80°  F.  for  the  month  of  July. 


DISCUSSION  OF  PLANT  INDUSTRIES          457 

and  therefore  a  more  profitable  crop.  Sweet  corn  contains 
more  sugar  in  the  grain  than  other  kinds,  particularly  when 
in  the  milk  stage.  It  is  much  grown  on  the  farm  for  home 
use,  and  by  market  gardeners  on  a  far  larger  scale  to  supply 
canning  establishments. 

419.  Wheat.  Wheat  is  the  most  highly  prized  of  the  cereals, 
and  has  been  cultivated  for  some  thousands  of  years  through- 
out large  parts  of  the  region  extending  from  China  to  southern 
and  western  Europe.    Most  people  prefer  wheat  preparations 
to  those  from  other  cereals.    Wheat  flour,  containing  a  large 
percentage  of  the  sticky  protein  material  known  as  gluten,  is 
particularly  well  adapted  for  bread-making. 

There  are  two  well-known  classes  of  wheats,  based  on  the 
time  of  sowing ;  spring  wheat,  which  is  planted  in  the  spring 
as  soon  as  the  ground  is  dry  and  warm  enough  for  tillage; 
and  winter  wheat,  which  is  planted  in  the  autumn,  grows  but 
little  before  winter,  finishes  its  growth  in  the  following  spring, 
and  is  harvested  in  the  summer.  Both  winter  and  spring 
wheats  include  hard  and  soft  varieties,  the  former  containing 
much  gluten  and  the  latter  less  gluten  but  more  starch.  The 
hardest  of  all  are  the  macaroni  wheats,  which  have  a  very 
high  food  value  but  are  not  usually  considered  well  adapted 
for  bread-making  unless  mixed  with  softer  wheats. 

Wheat  can  be  grown  in  a  cooler  climate  and  with  less  sum- 
mer rainfall  than  is  needed  for  corn.  For  semi-arid  regions, 
such  as  a  large  area  in  Texas  and  portions  of  Oklahoma  and 
Colorado,  the  macaroni  or  durum  wheats  are  extremely  well 
adapted.  Wheat  will  grow  well  on  a  more  clayey  soil  than  is 
best  for  corn,  and  in  general  throughout  the  corn  belt  the 
wheat  crop  takes  a  secondary  place,  often  being  planted  on 
land  that  for  some  reason  is  not  wanted  for  corn  growing.1 

420.  Other  cereals.    Oats,  rye,  and  barley  may  all  be  grown 
in  cooler  and  moister  climates  than  are  suited  for  corn  and 
wheat.  They  are  therefore  much  cultivated  in  northern  Europe. 

1  On  varieties  of  wheat  and  wheat  culture  see  Bulletin  24,  Division  of 
Vegetable  Physiology  and  Pathology,  U.  S.  Dept.  Agr.,  1900. 


458  PRACTICAL  BOTANY 

Oatmeal  cooked  in  various  ways,  barley  bread,  and  rye  bread 
are  therefore  more  used  than  wheat  by  the  poorer  classes 
throughout  that  region.  Oats  and  barley  are  both  much  used 
as  feed  for  horses,  and  barley  is  largely  employed  by  brewers 
in  the  manufacture  of  malt. 

Rice  is  the  great  cereal  crop  of  Asia,  and  a  good  deal  is 
grown  in  South  Carolina  and  the  Gulf  States.  The  territory 
in  which  rice  is  grown  has  been  much  extended  in  the  United 
States  within  the  past  decade.  The  crop  is  generally  cul- 
tivated on  land  that  is  overflowed  during  part  of  the  year 
(Fig.  274). 

421.  Grasses  cultivated  for    hay,  forage,  or  pasture.    In 
addition  to  the  high  value  already  stated  for  the  hay  crop, 
there  are  many  grasses  which  are  used  directly  as  feed,  with- 
out being  cut  and  dried  as  hay.    It  would  be  difficult  to  esti- 
mate the  annual  value  of  the  forage  grasses  and  the  pasturage 
of  the  United  States,  but  it  must  run  into  hundreds  of  millions 
of  dollars.    Only  three  or  four  of  the  most  important  grasses 
that  are  cultivated  or  somewhat  protected  in  their  growth  can 
here  be  mentioned. 

Timothy  is  the  leading  grass  for  hay,  especially  in  the  more 
northerly  states.  Redtop  ranks  next  after  timothy  as  a  source 
of  hay,  though  in  its  quality  it  is  somewhat  inferior  to  the 
former.  Kentucky  blue  grass  is  the  most  valuable  pasture 
grass  in  America.  There  are  many  grasses  of  great  value  in 
semi-arid  regions,  as  the  buffalo  grass.  Formerly  some  of 
these  dried,  as  they  stood,  into  a  kind  of  natural  hay  on  which 
the  vast  herds  of  buffalo  of  the  Great  Plains  fed  throughout 
the  winter.1  Red  clover  and  alfalfa  are  also  very  valuable 
hay-producing  plants.  They  do  not  belong  to  the  Grass  family, 
however,  but  to  the  Pea  and  Bean  family  (Leguminosse). 

422.  Cotton.    The  most  valuable  fiber  plant  of  the  world  is 
the  cotton  plant,  which  is  a  member  of  the  same  family  as  the 
mallows  and  the  hollyhocks.    It  is  grown  extensively  in  India, 

1  On  the  grasses  see  G.  F.  Warren,  Elements  of  Agriculture,  chap.  vii. 
The  Macmillan  Company,  New  York. 


DISCUSSION  OF  PLANT  INDUSTRIES  459 

Egypt,  and  in  our  own  Gulf  States.  In  1907  the  United 
States  produced  a  crop  worth  about  $675,000,000,  which  was 
approximately  three  fifths  of  the  world's  crop.  This  country 
ordinarily  produces  from  9,000,000  to  13,000,000  bales  of 
500  pounds  each,  the  total  value  ranging  from  one  third  to 
two  thirds  of  a  billion  dollars  in  value. 

The  cotton  consists  of  hairs  which  surround  the  seeds. 
Different  lengths  of  cotton  fibers  are  produced  by  different 
species.  There  is  also  much  variation  in  the  same  species  when 
grown  in  different  parts  of  the  world  and  under  more  or  less 
favorable  conditions.  The  cotton  plant  is  an  annual.  When 
grown  in  tropical  and  semi-tropical  countries  it  requires  a 
relatively  long  season  for  maturing.  In  regions  which  have 
shorter  growing  seasons  certain  kinds,  as  the  "  sea-island " 
cotton  (Grossypium  Barbadense),  will  mature  in  ninety  to  a 
hundred  days,  and  it  has  been  known  to  mature  in  seventy. 

423.  Fruits  of  the  Rose  family.    As  the  cereals  are  found 
in  the  Grass  family,  the  majority  of  fruits  are  found  in  the 
Rose  family.    A  large  proportion  of  the  edible  fruits  of  the 
temperate  region  (using  the  word  fruit  in  its  popular  sense) 
is  produced  by  this  family.    These  fruits  may  be  divided 
into  (1)  pome  fruits,  such  as  the  apple,  pear,  and  quince ; 

(2)  "  berries,"  which  are  fruits  that  are  commonly  but  in- 
correctly called  berries,  as  the  blackberry  and  strawberry ; 

(3)  stone  fruits,  such  as  the  peach,  apricot,  plum,  and  cherry. 

424.  The  pome  fruits.    Apples  are  the  most  important  rosa- 
ceous fruits.    They  have  been  cultivated  for  several  thousand 
years.    The  wild  species  from  which  they  are  thought  to  have 
originated,  flourished  in  ancient  times  over  a  large  area  in  the 
region  about  the  Caspian  and  Black  seas  in  southern  Europe. 
This  supposed  ancestral  apple  is  still  represented  by  wild 
forms  that  live  in  Europe,  the  fruit  of  which  is  small,  hard, 
extremely  sour,  and  unpalatable.    From  the  original  wild  form 
thousands  of  different  kinds  have  developed,  and  these  range 
to  such  extremes  in  size,  color,  quality,  and  time  of  ripening, 
that  it  is  difficult  to  conceive  of  them  as  having  a  common 


460  PEACTICAL  BOTANY 

ancestry.  Cultivation  has  increased  the  bulk  of  the  fruit  sev- 
eral hundred  times;  moreover,  in  the  plants  now  cultivated 
only  one  flower,  or  a  few  flowers,  of  the  cluster  develop  fruit, 
as  is  also  the  case  with  the  pear.  The  importance  of  the  apple 
industry  may  be  realized  from  the  fact  that  a  full  crop  for 
the  United  States  and  Canada  amounts  to  about  100,000,000 
barrels. 

Apples  are  grown  on  a  large  scale  in  most  of  the  cooler 
portions  of  the  United  States,  but  there  are  large  areas  of 
good  orchard  land  not  thus  utilized,  particularly  in  the  cen- 
tral Appalachian  region.  Apple  growing  in  irrigated  lands  is 
rapidly  increasing  in  the  United  States. 

Pears  are  much  less  extensively  grown  than  apples.  Cali- 
fornia pears,  as  is  well  known,  are  usually  the  largest  and  the 
finest  that  are  grown.  It  is  interesting  to  note  that  while  the 
finest  pears  consumed  in  England  were  formerly  of  French 
growth,  the  United  States  is  now  exporting  pears  for  the 
English  market.  Quinces  are  not  of  much  commercial  impor- 
tance, being  used  for  little  else  than  as  a  basis  for  preserves 
and  jellies.  A  large  part  of  those  produced  are  ordinarily 
grown  for  home  use  on  one  or  two  trees  in  a  corner  of  the 
garden  or  orchard. 

425.  "  Berries. "  In  the  so-called  berries  of  the  Rose  family 
the  ovaries  ripen  together,  forming  a  thimble-shaped  fruit 
upon  the  end  of  the  flower  stem,  or  receptacle,  as  in  the  black- 
berry; or  it  may  be  the  receptacle  itself  which  ripens,  and, 
with  its  seeds  upon  its  surface,  forms  the  fruit,  as  is  true  in 
the  strawberry. 

Cultivated  strawberries  are  mostly  descended  from  a  Pacific 
coast  species  which  was  introduced  into  cultivation  from  Chile 
some  two  hundred  years  ago.  The  plant  occurs  wild  along 
the  North  American  coast  as  far  north  as  Alaska.  Strawberry 
growing  in  the  United  States  began  with  the  once  famous 
Hovey  seedling,  about  1834  or  1835,  but  was  of  little  impor- 
tance until  after  1840.  Strawberries  grow  readily  in  almost 
all  good  farming  lands  of  the  country.  In  favorable  situations 


DISCUSSION  OF  PLANT  INDUSTRIES          461 

the  crop  is  very  profitable,  as  the  yield  may  exceed  four  hun- 
dred bushels  per  acre.  Strawberry  raising  on  a  large  scale  was 
long  confined  chiefly  to  gardens  in  the  neighborhood  of  cities 
which  served  as  a  market.  With  improved  quality  and  better 
facilities  for  shipping  it  has  now  become  an  extensive  indus- 
try, and  the  season  for  some  consumers  has  been  extended 
from  a  few  weeks  to  five  or  more  months,  beginning  in  Jan- 
uary with  the  product  of  the  Gulf  States  and  ending  in  July 
with  Canadian  berries. 

There  are  at  least  five  species  of  raspberries  in  cultivation, 
but  none  of  them  bear  transportation  especially  well.  They 
are  grown  considerably  for  shipment  over  comparatively  short 
distances.  The  red  species,  whether  wild  or  cultivated,  is  much 
used  in  preserving-factories  in  making  jam,  and  at  times  is 
prominent  in  the  fruit  markets. 

Blackberries,  of  which,  including  the  Pacific  coast  forms, 
there  are  five  or  more  species  in  cultivation,  are  known  as 
commercial  fruit  only  in  America.  Their  cultivation  began 
before  1841,  and  was  slow  to  reach  its  present  importance. 
Most  of  the  favorite  varieties  were  for  years  only  chance 
seedlings  of  the  upright  wild  species,  but  at  present  improved 
kinds  that  are  descended  from  the  trailing  dewberries  are 
coming  into  favor. 

426.  Stone  fruits.  Our  most  common  stone  fruits  are 
peaches,  plums,  and  cherries.  Of  these  three  fruits  the  two 
latter  occur  wild,  but  only  plums  have  been  much  used  in  the 
wild  state.  Of  the  thousands  of  acres  of  wild-plum  thickets 
once  widely  scattered  over  the  Middle  West,  few  now  remain. 

Peaches  are  of  Chinese  origin,  and  were  early  introduced 
into  America  from  Europe.  They  cannot  be  safely  cultivated 
except  where  there  is  little  danger  of  frosts  after  the  trees 
have  blossomed.  Favorite  peach-growing  portions  of  the 
United  States  are  the  southerly  part  of  the  region  bordering 
the  Great  Lakes,  parts  of  Georgia  and  Alabama,  southern 
Illinois,  Missouri  and  Kansas,  western  Colorado,  Texas, 
and  most  of  California  except  the  mountainous  portion.  As 


462  PRACTICAL  BOTANY 

peaches  are  yery  perishable,  most  of  the  crop  (as  is  the  case 
with  strawberries)  must  be  taken  to  market  in  refrigerator  cars. 

Nectarines,  apricots,  and  almonds  are  very  closely  related 
to  peaches. 

Plums,  cultivated  in  various  parts  of  the  United  States, 
belong  to  about  ten  groups,  of  Asiatic,  European,  and  Ameri- 
can origin.  Some  highly  successful  varieties  are  of  hybrid 
origin  (Fig.  341).  One  of  these  is  derived  from  the  little 
beach  plum1  so  well  known  along  the  Atlantic  coast,  and 
the  common  wild  plum2  which  ranges  from  New  England 
to  Colorado  and  Texas.  This  hybrid  is  extraordinarily  hardy 
and  prolific.  Among  the  most  valuable  plums  are  those  which 
can  be  dried  whole  for  prunes,  and  these  are  now  extensively 
grown  in  California. 

Cherries  in  cultivation  are  of  two  types,  the  sour  and  the 
sweet,  both  derived  from  European  species.  The  sour  varie- 
ties are  grown  throughout  a  large  portion  of  the  country,  the 
sweet  ones  principally  in  California. 

427.  Citrous  fruits.  The  plants  which  bear  oranges,  grape- 
fr,uit,  and  lemons,  are  not  hardy  but  thrive  in  tropical  or  semi- 
tropical  climates.  They  may  grow  in  regions  where  frosts  are 
rare  and  light.  In  the  United  States  the  leading  citrous-fruit 
orchards  are  in  Florida  and  California.  The  wild  orange  is 
probably  a  native  of  southeastern  Asia.  Its  fruit  is  sour,  but 
the  tree  is  more  hardy  than  some  of  the  improved  sweet  varie- 
ties. Because  of  this  hardiness  the  sweet  varieties  are  some- 
times grafted  upon  the  wild  stock  in  order  to  make  use  of  the 
stronger  wild  plants.  By  means  of  experiment  and  cultivation 
many  hundreds  of  varieties  of  oranges  have  been  produced. 
Attempts  are  still  being  made  to  produce  trees  which  will 
withstand  the  colder  winters  of  the  region  farther  north  and 
at  higher  altitudes  than  where  they  are  now  grown.  These 
efforts  have  been  partially  successful. 

Oranges,  lemons,  and  the  grapefruit  or  pomelo,  as  well  as 
the  more  recently  developed  varieties,  as  the  tangerine  and 

1  Prunus  maritima.  2  Prunus  americana. 


DISCUSSION  OF  PLANT  INDUSTKIES  463 

kumquat,  have  peculiarly  valuable  shipping  qualities,  which 
make  it  possible  for  these  fruits  to  be  shipped  anywhere  and 
to  be  kept  for  very  long  periods. 

428.  The  grapes.  The  fruit  of  the  grape  is  known  to  have 
been  used  by  the  earliest  civilized  peoples.  From  the  wild 
grapes,  which  though  sour  are  edible,  more  than  a  thousand 
varieties  have  been  developed.  These  differ  in  color,  as  white, 
black,  blue,  or  red ;  and  in  texture,  from  the  soft  juicy  grapes 
from  which  wine  is  made,  to  the  more  solid  ones  which  are 
dried  in  making  raisins.  The  leading  grape-producing  states 
are  New  York,  Ohio,  Michigan,  and  California. 

Perhaps  the  best-known  and  the  most  widely  distributed 
kind  of  cultivated  grape  that  is  native  to  the  United  States  is 
the  Concord  grape,  which  was  discovered  by  Ephraim  Bull  at 
Concord,  Massachusetts.  Part  of  the  original  vine  still  grows 
on  the  lawn  of  the  old  Ephraim  Bull  homestead. 

The  European  grapes,  which  form  the  basis  of  the  very  large 
and  important  wine  industries  of  France,  were  developed  out 
of  a  different  stock  from  that  of  the  American  cultivated 
grapes.  Since  the  French  grapes  produced  a  quality  of  wine 
that  differed  from  that  made  from  the  grapes  of  the  United 
States,  European  grapes  were  brought  to  this  country.  Their 
roots  were  soon  attacked,  and  the  plants  well-nigh  destroyed, 
by  a  small  parasitic  insect  known  as  phylloxera  (Sect.  343). 
It  was  found,  however,  that  the  roots  of  the  American  grapes 
were  able  to  withstand  attacks  from  phylloxera  and  were  not 
seriously  affected  by  it.  It  was  also  found  that  when  Euro- 
pean grapes  were  brought  to  this  country  and  grafted  upon 
American  stock,  the  quality  of  the  European  fruit  might  be 
secured  without  the  accompanying  dangers  from  the  insect. 
But  when  grape  growers  transplanted  American  grapes  into 
Europe  the  phylloxera  was  also  transferred,  and  soon  the  na- 
tive grapes  of  Europe  were  attacke.d  and  serious  damage  was 
done  in  the  vineyards  of  France.  In  order  to  protect  their 
vineyards  many  French  grape  growers  adopted  the  practice 
of  planting  American  plants  and  then  grafting  their  own 


464  PRACTICAL  BOTANY 

grapes  upon  this  introduced  stock.  The  grape  industry  of 
France  has  been  greatly  increased  by  thus  growing  French 
grapes  upon  the  stronger  and  more  productive  American  stock. 
Some  French  grape  growers,  still  believing  that  the  quality 
of  their  grapes  would  deteriorate  if  grown  upon  American 
stock,  use  carbon  disulphide  as  a  means  of  protection  against 
phylloxera,  but  this  treatment  is  still  too  expensive  to  be 
used  in  the  ordinary  vineyards. 

429.  Garden  vegetables.  Another  group  of  plants  which  form 
the  basis  of  a  great  industry  includes  those  generally  known 
as  vegetables.  The  vegetables  come  from  many  plant  families. 
According  to  one  authority,1  there  are  at  least  two  hundred 
eleven  distinct  species  of  garden  vegetables,  and  many  of  these 
species  are  represented  by  very  large  numbers  of  varieties.  The 
parts  of  these  plants  used  as  food  may  be  the  roots  (sweet 
potato,  radish,  etc.),  the  combined  stem  and  root  (beet,  parsnip, 
carrot),  the  underground  stem  (white  potato,  Jerusalem  arti- 
choke), stem  and  leaves  (lettuce,  cabbage),  and  the  fruit  (to- 
mato, squash,  cucumber,  eggplant,  string  beans).  The  list  of 
vegetables  is  too  long  and  varied  for  any  common  characters 
to  be  given  for  it. 

1  Vilmorin,  in  The  Vegetable  Garden. 


CHAPTER  XXV 
WEEDS 

430.  What  is  a  weed  ?  It  is  not  possible  to  put  into  a  short 
sentence  a  complete  statement  of  what  is  meant  by  a  weed. 
It  is  often  said  that  a  weed  is  a  plant  that  is  not  wanted. 
Perhaps  a  better  definition,  from  the  farmer's  point  of  view, 
would  be :  A  weed  is  a  plant  which  interferes  with  some  crop. 
The  word  crop  must,  in  this  case,  be  taken  in  a  very  gen- 
eral sense.  The  dandelions  which  interfere  with  the  growth 
of  grass  on  a  lawn,  or  the  raspberry  bushes  which  spring  up 
in  burnt-over  clearings  in  white-pine  woods  and  crowd  out 
young  tree  seedlings,  must  be  reckoned  as  truly  weeds  as 
the  ragweeds  and  the  pigweeds1  that  are  so  troublesome  in 
cornfields. 

Cultivated  plants  may  become  very  injurious  weeds.  Horse- 
radish, and  Johnson  grass,2  which  is  valued  in  the  South  as  a 
hay  plant,  are  good  instances  of  this. 

In  the  ordinary  sense  the  term  weed  is  applied  only  to 
flowering  plants  or  to  the  larger  representatives  of  the  lower 
groups,  such  as  ferns  and  horsetails.  The  many  bacteria  and 
higher  fungi  which  do  so  much  harm  in  the  farm  and  garden 
are  never  spoken  of  as  weeds. 

431.  Classes  of  weeds.    Weeds  may  be  classified  in  many 
ways,  according  to  the  kinds  of  resemblances  and  differences 
taken  into  account  in  grouping  them.3   The  kind  of  classifica- 
tion which  would  first  suggest  itself  to  most  botanists  is  that 
into  families,  such  as  the  Grass  family,  the  Nettle  family,  and 
the  Buckwheat  family.    Another  kind  of  division  would  be 
into  annual,  biennial,  and  perennial  plants ;  still  another  into 

1  Amaranthus.  2  Sorghum  halepense. 

8  See  Percival,  Agricultural  Botany,  Part  V.  Henry  Holt  &  Co.,  New  York. 

465 


466 


PRACTICAL  BOTANY 


sun  plants  and  shade  plants,  or  into  drought-enduring  and 
moisture-loving  plants  (Sects.  441-446).  We  are  fortunately 
as  yet  but  little  troubled  in  this  country  by  one  obnoxious 
group  of  weeds,  the  parasitic  flowering  plants.  The  clover 

dodder  (Fig.  351)  is  one 
of  the  most  important  of 
these,  causing  much  trou- 
ble in  fields  of  clover  and  of 
alfalfa.  The  farmer  would 
often  class  weeds  accord- 
ing to  the  kind  of  crop  with 
which  they  interfere;  for 
example,  into  weeds  of  pas- 
tures and  those  of  culti- 
vated ground,  subdividing 
the  latter  group  into  weeds 
of  cornfields,  weeds  of  oat 
and  wheat  fields,  weeds  of 
clover  fields,  and  others. 

432.  Qualifications  for  suc- 
cessful weeds.  Not  many 
wild  plants  of  any  region 
can  become,  even  in  the  ter- 
ritory to  which  they  are 
native,  successful  weeds. 
The  trilliums,  columbines, 

A,  habit  sketch  of  part  of  the  parasite  and  pepperroots,  fire  pinks,  wild 

the  host ;  B,  portion  of  stem  of  the  dodder,  ginger  (Fig.  43),  Dutdl- 

showing  protuberances  from  which  haus-  ,     i            i                  i        •-,  -t 

toria  pass  into  the  stem  of  the  host;   C,  man  S-breecheS,   and  Wild 

a  single  flower  of  the  dodder.    B  and  C  SW66t  William  {Phlox),  SO 

familiar  among  the  early 
wild  flowers  of  the  Middle 
West,  are  there  practically  unknown  in  cultivated  fields.  For 
various  reasons  the  conditions  of  life  in  tilled  ground  are 
promptly  fatal  to  them.  In  order  to  push  its  way  among  com- 
petitors, to  win  in  the  struggle  for  existence,  under  natural 


FIG.  351.  Clover  dodder,  parasitic  on 
red  clover 


considerably   magnified.    Modified   after 
"  Flora  Danica  " 


WEEDS 


467 


conditions  and  with  the  farmer  and  gardener  against  it,  the 
weed  must  possess  exceptional  powers  of  reproduction  or  of 


FIG.  352.  J.,  corn  cockle,  a  weed  of  the  Pink  family,  troublesome  in  grain- 
fields.    The  seeds  are  poisonous.    One  third  natural  size.    .B,  cocklebur,  a 
very  troublesome  weed  of  the  Composite  family,  in  rich  land  throughout 
a  large  part  of  the  country.   Two  thirds  natural  size 

resistance  to  unfavorable  influences.    Some  of  the  chief  quali- 
fications which  distinguish  weeds  are : 

(1)  The  power  of  vegetative  reproduction. 

(2)  Deep,  tough  roots,  or  relatively  extensive  development 
of  the  underground  portion. 

(3)  The  power  to  produce  many  seeds. 


468  PRACTICAL  BOTANY 

(4)  Capacity  for  self-pollination  (if  necessary). 

(5)  Good  means  of  seed  dispersal. 

(6)  Capacity  for  rapid  growth. 

(7)  The  ability  to  resist  plant  diseases. 

(8)  Tolerance  of  shade  (at  least  when  young). 

(9)  Tolerance  of  drought. 

(10)  Tolerance  of  excessive  water  supply  and  lack  of  air 
in  the  soil. 

(11)  The  ability  to  resist  the  effects  of  dust  in  choking 
the  stomata. 

(12)  Capacity  to  thrive  in  poor  soil. 

(13)  Ability  to  retain  vitality  of  seeds  buried  in  the  soil, 
sometimes  from  fifteen  to  twenty-five  years. 

(14)  Unpalatableness,  offensive   smell,  prickles,  or  other 
disagreeable  characteristics,  which  lessen  the  danger  of  being 
eaten  by  animals. 

Few  if  any  weeds  have  all  the  above-named  characteristics 
in  a  high  degree,  but  many  kinds  of  plants  have  the  greater 
part  of  them.  Which  characteristics  are  common  to  many 
weeds  of  woodlands?  of  pastures?  of  lawns?  of  roadsides? 
of  cornfields?  of  fields  of  the  small  grains?  Name  some  of 
the  weeds  which  you  know  that  have  the  largest  number  of 
the  qualifications  (1)-(14).  Can  you  name  any  plant  that 
has  both  characteristics  (9)  and  (10)  ? 

433.  Effectiveness  of  weed  equipment.  In  most  instances  it 
is  easy  to  see  how  the  characteristics  listed  in  Sect.  432  enable 
weeds  to  persist.  Evidently  a  plant  which,  like  the  Russian 
thistle,  produces  tens  of  thousands  of  seeds,  or  one  which, 
like  the  dandelion,  scatters  seeds  for  miles  with  the  wind,  is 
likely  to  reproduce  itself  abundantly  and  to  occupy  any  suit- 
able bit  of  vacant  ground.  But  there  are  other  most  effec- 
tive qualifications  which  need  a  little  explanation.  If  a  sorrel 
plant 1  (Fig.  353)  is  dug  up  carefully,  it  will  usually  be  found 
to  have  several  others  attached  to  it  by  the  roots.  This  is 
rapidly  becoming  one  of  the  worst  weeds  in  the  United  States, 
1  Rumex  Acetosella. 


WEEDS 


469 


being  especially  abundant  in  slightly  acid  soils.  Many  other 
kinds  of  plants,  from  nettles  to  goldenrods,  are  joined  in 
colonies  by  long  underground  stems.1  The  sorrel  roots  and 
the  goldenrod  rootstocks  produce  many  buds,  and  each  bud 
may  grow  into  a  new  plant.  If  the  rootstock  is  cut  to  pieces 
with  a  hoe,  the  process  of  reproduction  is  only  urged  on  a 
little.  Every  tuber  of  some  sunflowers  (Fig.  67), 
the  nut  grass,  and  many  other  tuber-bearing 
plants  may  grow  into  a  new  individual.  Purs- 
lane plants  when  hoed  up  and  left  on  damp 
soil  at  once  begin  to  grow,  each  bit  forming  a 
successful  cutting.  These  are  only  a  few  of 
the  hundreds  of  examples  that  might  be  given 
of  vegetative  reproduction 
among  weeds. 

The  way  in  which  fox- 
tail grass  maintains  itself 
in  grainfields,  making  slow 
growth  while  it  is  over- 
topped by  the  wheat,  oats, 
or  rye,  and  then  pushes 
up  rapidly,  flowering  and 
seeding  among  the  stubble, 
is  an  excellent  illustration 
of  the  importance  to  the 
plant  of  the  power  to  tol- 
erate shade  during  the  early  period  of  growth.  It  must  be 
remembered  that  any  qualification  that  helps  the  weed  in  its 
struggle  for  existence  is  a  good  thing  for  the  weed,  even  if  it 
is  discouraging  from  the  point  of  view  of  the  farmer. 

The  survival  of  mullein  and  ironweed  in  pastures,  and  of 
dog  fennel,  smartweeds,  and  the  offensive-smelling,  poisonous 
Jimson  weeds  (Fig.  300)  in  barnyards,  are  only  a  few  examples 
of  the  many  that  could  be  given  to  show  how  some  weeds 
persist  by  being  uneatable  or  positively  offensive. 
1  See  Bulletin  76,  Kansas  Agr.  Exp.  Sta. 


FIG.  353.  Portion  of  a  plant  of  the  com- 
mon sorrel 

The  leaf  is  drawn  about  one  half  natural 

size.  The  running  roots  of  a  large  specimen 

would  be  at  least  sixty  times  as  long  as  the 

piece  here  shown 


470  PRACTICAL  BOTANY 

434.  How  weeds  injure  the  farm  and  garden.1  Although 
some  weeds  are  of  use  as  food  for  man  or  the  lower  animals 
and  a  few  have  medicinal  properties,  their  presence  in  the 
farm  or  garden  is  on  the  whole  most  harmful  in  the  follow- 
ing ways : 

(1)  Weeds  take  soil  moisture  needed  by  useful  plants. 

(2)  Weeds  rob  the  soil  of  valuable  salts,  such  as  nitrates 
and  potash  compounds,  and  it  is  probable  that  they  may  add 
secretions  that  are  injurious. 

(3)  Weeds  weaken  other  plants  by  shading  them,  thus  hin- 
dering photosynthesis. 

(4)  Parasitic  weeds,  like  the  flax  dodder  and  the  clover 
dodder  (Fig.  351),  rob  their  hosts  of  plant  food. 

(5)  Some  weeds  harbor  parasitic  fungi  or  insects  injurious 
to  useful  plants. 

(6)  Poisonous  or  intoxicating  plants  injure  horses,  cattle, 
and  sheep. 

(7)  Some  spiny  plants,  such  as  the  smaller  cacti,  and  burs 
like  the  sand  bur,  may  lame  the  feet  of  domestic  animals. 
Thorny  shrubs  are  very  troublesome  to  woolgrowers,  pulling 
out  much  wool,  and  burs  greatly  injure  the  quality  of  the  fleece. 

(8)  Certain  weeds,  when  eaten  by  cows,  render  milk  un- 
palatable or  ill-scented. 

(9)  Weed  seeds  injure  the  quality  and  affect  the  price 
of  clover  and  other  seeds  that  are  raised  for  sale,  and  thus 
diminish  the  value  of  the  grain  with  which  they  are  mixed. 

The  harm  done  by  weeds  in  shading  crops  is  most  notice- 
able in  the  case  of  rapidly  growing  species  which  spring  up 
among  delicate  seedlings  such  as  flax  and  onions.  In  extreme 
cases  the  weeds  may  almost  entirely  prevent  the  growth  of 
the  crop. 

The  most  important  example  of  fungi  harbored  by  weeds 
is  that  of  wheat  rust  on  barberry  bushes  (Sect.  233).  The 
potato  beetle  feeds  on  many  plants  of  the  Nightshade  family, 

1  See  Bulletin  175,  " A  Second  Weed  Manual,"  Ohio  Agr.  Exp.  Sta.,  for  a 
fuller  discussion. 


WEEDS 


471 


and  then  transfers  itself  to  any  neighboring  potato  plants 
that  are  not  protected  by  applications  of  Paris  green  or  of 
other  poisons. 

A  familiar  example  of  a  pasture  weed  poisonous  to  the 
lower  animals  is  the  common  sheep  laurel  or  lambkill.1  There 
are  a  good  many  plants,  such  as  some  members  of  the  Night- 
shade family,  hemp,  and  some  leguminous  species,2  which  may 
produce  symp- 
toms both  of 
intoxication  and 
of  poisoning  in 
horses,  sheep,  and 
cattle. 

Of  the  plants 
which  give  a  bad 
taste  to  milk, 
field  garlic  or 
wild  onion3  is  the 
most  important. 
The  bulblets  of 
this  weed  may 
also  impart  an 
onion  flavor  to 
flour  made  from 
wheat  grown  in 

fields  infested  with  it.  As  an  instance  of  the  extent  to  which 
weed  seeds  may  contaminate  commercial  samples  of  useful 
seeds,  the  case  of  red  clover  may  be  cited.  Inferior  lots  of 
clover  seed  may  contain  as  much  as  67  per  cent  of  impurities, 
largely  other  seeds,4  and  the  average  of  84  samples  examined 
at  the  Iowa  station  was  5  per  cent,  or  3  pounds  to  the  bushel. 
In  the  red  and  mammoth  clover  seed  examined  at  a  single 

1  Kalmia  angustifolia. 

2  The  so-called  "loco  weeds,"  mostly  species  of  Astragalus  and  Aragallus. 

3  Allium. 

*  See  Bulletin  21,  Iowa  Agr.  Coll.  Exp.  Sta. 


FIG.  354.  Horse  nettle  (Solarium  carolinense) 

A  very  troublesome  weed  of  the   Nightshade  family, 

which  has  spread   extensively   from   the   southeastern 

states.   One  half  natural  size 


472  PRACTICAL  BOTANY 

agricultural  experiment  station  there  were  found  in  all  87 
species  of  other  seeds,  mostly  those  of  noxious  weeds,  belong- 
ing to  23  different  families  of  plants.1 

435.  Other  injuries  caused  by  weeds.  Aside  from  the  dam- 
age inflicted  by  weeds  upon  growing  crops  and  farm  animals, 
much  harm  is  done  by  them  in  less  obvious  ways. 

Roadside  weeds  of  many  species  encroach  upon  roads  of  all 
kinds,  from  country  byways  to  city  boulevards.  Among  the 
weeds  of  waste  ground  there  are  many  which  disfigure  the 
surface  of  vacant  city  lots,  and  the  numerous  burs  among 
them  load  the  passer  with  their  clinging  seeds  or  fruits. 

Railway  rights  of  way,  if  left  uncared  for,  soon  become  over- 
grown with  weeds,  which  shade  the  ties  and  cause  them  to 
decay  more  rapidly.  It  is  estimated  that  the  expense  of  re- 
moving weeds  from  the  railway  tracks  in  the  state  of  Ohio 
alone  exceeds  $500,000  a  year. 

Streams,  canals,  and  drainage  or  irrigation  ditches  are  often 
infested  by  weeds,  which  may  almost  stop  the  current  of  water 
in  them.  The  water  weed,  or  ditch  moss  (Elodea),  introduced 
into  Europe  from  America,  has  become  a  nuisance  there,  choking 
small  streams  with  its  abundant  growth.  The  so-called  water 
hyacinth  (Eiclihornia)  from  South  America,  often  cultivated 
in  aquaria  and  small  ponds,  has  been  introduced  into  Florida 
and  other  southern  waters,  where  it  greatly  impedes  navigation. 

436.  The  origin  and  dissemination  of  weeds.    One  of  the 
interesting  facts  with  which  the  young  botanist  is  first  im- 
pressed on  beginning  to  identify  weeds  and  to  trace  their  his- 
tory, is  the  extent  to  which  they  have  immigrated  from  other 
countries.2    No  one  can  calculate  with  exactness  the  propor- 
tion of  our  weeds  (that  is,  of  individuals)  which  have  been 
brought  in  from  other  countries.    But  it  is  not  difficult  to  see 
how  the  numbers  stand  in  comparing  native  and  introduced 

1  See  Bulletin  175,  Ohio  Agr.  Exp.  Sta. 

2  See  the  article,  "Pertinacity  and  Predominance  of  Weeds,"  in  the 
Scientific  Papers  of  Asa  Gray,  selected  by  C.  S.  Sargent,  Vol.  II,    Houghton 
Mifflin  Company,  Boston  ;  also  Farm  Weeds  of  Canada,  Second  Edition, 
Government  Printing  Bureau,  Ottawa,  Canada. 


WEEDS 


473 


species,  if  we  look  through  a  list  of  a  hundred  of  the  worst 
weeds  over  the  continental  area  of  the  United  States  (exclud- 
ing Alaska),1  it  appears  that  almost  exactly  half  of  the  num- 
ber are  from  Europe.  Nine  others  are  from  tropical  America 
or  from  India,  so  that  a  clear  majority  of  these  hundred  nota- 
ble weeds  are  foreigners.  It  is  rather  difficult  to  give  all  the 
reasons  why  so  many  of  our  common  weeds  come  from  Europe, 

but  it  is  certain  that  of  the 
prevalent  weeds  on  that  con- 
tinent  many  represent   the 
result  of  a  gradual  sifting- 
out    process 
which   has 
lasted    for 
tens  of  cen- 
turies. Dur- 
ing all  that 
long   period 
the  tilled 
lands  of  Eu- 
rope   have 

gradually  become  populated  by  such  European  plants  as  proved 
able  to  live  in  cultivated  ground  in  a  temperate  climate  against 
human  opposition.  Together  with  these  are  found  such  other 
persistent  species  as  may  have  found  their  way  in  from  Asia 
and  Africa.  When  the  soil  of  temperate  North  America  first 
began  to  be  cultivated  by  the  whites,  it  was  inevitable  that 
great  numbers  of  European  weeds  should  be  brought  in  along 
with  farm  and  garden  seeds,  in  the  ballast  of  vessels,  and  in 
other  ways,  and  rapidly  gain  a  foothold  on  the  new  continent. 
The  history  of  the  spread  of  many  weeds  has  been  preserved, 
and  it  forms  a  most  interesting  chapter  of  economic  botany.2 

1  Farmers'  Bulletin  28,  U.  S.  Dept.  Agr. 

2  See  the  essay  of  Dr.  Gray  already  cited ;  also  Farmers'  Bulletin  28  and 
Bulletin  15,  Division  of  Botany,  U.  S.  Dept.  Agr.  Consult  also  all  the  attain- 
able weed  reports  of  the  state  agricultural  experiment  stations. 


FIG.  355.  Pokeweed,  a  common  weed  of  waste  ground 
A,  a  flowering  branch ;  B,  flower ;  C,  fruit 


474  PRACTICAL  BOTANY 

It  is  a  well-known  fact  that  new  weeds  are  particularly 
likely  to  be  found  in  places  where  ballast  from  vessels  is 
dumped,  where  cargoes  of  foreign  grain  are  cleaned,  and 
where  foreign  wool  is  scoured  and  cleaned  from  burs  and 
other  seeds.1  Some  very  troublesome  weeds,  as  the  common 
carrot  and  the  orange  hawkweed,  have  been  cultivated  for  use 
or  ornament  and  escaped  into  fields,  meadows,  and  pastures. 

437.  Weeds  of  various  regions.  Any  two  regions  which 
differ  widely  in  soil  or  climate  are  sure  to  differ  also  in  the 
weeds  which  predominate  there.  Such  tropical  plants  as  the 
sensitive  plant2  and  the  rosy  periwinkle,3  not  uncommon  in 
our  greenhouses  and  gardens,  are  troublesome  weeds,  the  for- 
mer in  tropical  South  America  and  the  islands  of  the  South 
Pacific,  and  the  latter  in  the  West  Indies.  But  in  our  climate 
it  requires  care  and  protection  to  keep  them  alive.  Even  in 
the  various  climates  afforded  by  the  United  States,  there  is 
range  enough  to  make  one  weed  troublesome  in  one  portion 
of  the  country  and  another  in  another  portion.  The  quack 
grass,  or  couch  grass,4  so  injurious  from  its  creeping  rootstocks 
in  fields  and  gardens  from  Maine  to  Minnesota,  is  replaced  as 
a  weed  in  the  southern  states  by  the  Johnson  grass,5  which 
has  still  stronger  and  longer  rootstocks.  The  wild  gourd,6 
troublesome  in  the  far  Southwest,  is  not  found  as  a  weed 
northeast  of  California  and  New  Mexico,  and  the  cacti,7  an- 
noying weeds  in  central  and  southern  Kansas  and  westward 
and  southward,  are  of  no  importance  farther  east. 

The  amount  of  moisture  in  the  soil  is  an  important  factor 
in  the  distribution  of  weeds.  Such  plants  as  the  cacti  just 
mentioned,  some  cinquefoils,  St.-John's-worts,  lambkill,  some 
species  of  vervain,8  the  common  mullein,  rib  grass,9  and  the 

1  A  curious  case  of  distribution  of  a  bur  is  that  of  the  grass  Andropogon 
acicularis.  A  buffalo  with  his  hair  filled  with  the  needle-like  fruits  of  this  grass 
was  sent  as  a  present  to  the  so-called  king  of  Ternate,  in  the  Malay  Archi- 
pelago.   From  this  one  animal  the  grass  soon  spread  over  the  whole  island. 

2  Mimosa  pudica.        3  Vinca  rosea.        4  Agropyron  repens.        6  Sorghum 
halepense.      6  Cucurbita  perennis.      7  Mamillaria,  Opuntia,  and  other  genera 
in  the  Southwest.      8  Verbena.      9  Plantago  aristata  and  P.  lanceolate. 


WEEDS  475 

everlastings  are  especially  frequent  in  dry  pastures.  A  few 
ferns,  such  as  the  sensitive  fern  and  the  ostrich  fern,1  horse- 
tails, rushes,  sedges,  many  worthless  coarse  grasses,  smart- 
weeds,  docks,  some  buttercups,  mints,  and  the  ironweeds  are 
common  only  in  moist  fields,  meadows,  and  pastures. 

438.  How  to  avoid  weeds.  The  methods  of  destroying  weeds 
are  fully  discussed  in  treatises  on  agriculture.  A  great  deal  can 


FIG.  356.  Tumbleweeds  (Cycloloma)  drifted  into  heaps  by  the  wind 

be  done  toward  the  prevention  of  weeds  by  taking  pains  not 
to  use  poor  seed  for  the  farm  and  garden,  since  the  cheaper 
kinds  often  contain  many  weed  seeds.  Stable  and  barnyard 
manure  frequently  contains  many  seeds  of  the  most  objection- 
able weeds,  and  in  caring  for  lawns  it  is  often  found  cheaper 
to  use  ground  bone  or  chemical  fertilizers,  such  as  superphos- 
phate of  lime,  than  to  spread  over  the  grass  fertilizers  which 
may  introduce  multitudes  of  troublesome  weeds. 

One  of  the  most  obvious  means  of  keeping  one's  premises 
free  from  weeds  is  not  to  allow  them  any  avoidable  breeding 

1  Onoclea. 


476  PRACTICAL  BOTANY 

places.  All  fence  rows,  hedges,  clumps  of  blackberry  and 
raspberry  bushes,  and  similar  lurking  places  for  weeds,  as  well 
as  grassland  and  tilled  ground,  should  be  kept  as  clean  and  as 
nearly  weedless  as  possible.  Weeds  which  have  gone  to  seed 
should  not  be  plowed  or  spaded  under,  but  allowed  to  dry 
and  then  burned.  It  will  be  found  well  worth  while  to  rake 
away  from  fences  and  burn  all  such  accumulations  of  tumble- 
weeds  as  those  shown  in  Fig.  356.  Wild  mustard,  which  is  a 
very  troublesome  weed  in  fields  of  the  small  grains,  is  read- 
ily killed  by  spraying  with  a  solution  of  copper  sulphate  or 
iron  sulphate.  Weedy  lawns  are  sometimes  improved  by  very 
careful  salting,  which  does  not  injure  the  grass.  Gravel  walks 
may  be  cleared  of  weeds  by  watering  them  with  a  solution  of 
sodium  arsenate  or  of  crude  carbolic  acid. 


CHAPTER  XXVI 


ECOLOGICAL  GROUPS;  REGIONAL  DISTRIBUTION  OF  PLANTS! 

439.  Ecology  in  earlier  chapters.  The  term  ecology  has 
already  been  denned  (Sect.  110).  In  the  preceding  chapters 
of  this  book  the  ecology  of  the  plant  has  usually  been  some- 
what discussed  along 
with  the  account  of  the 
plant  itself  and  of  its  or- 
gans. For  instance,  much 
of  what  was  said  about 
the  relations  of  the  root 
to  the  soil  (Chapter 
III),  root-tubercle  bac- 
teria (Chapters  III  and 
XXIV),  mycorrhiza 
(Sect.  38),  and  the  rela- 
tions of  stem  and  leaf 
to  light  supply  (Chapter 


FIG.  357.  The  duckweed,  one  of  the  simplest 
floating  seed  plants 


IV)  is  a  part  of  plant 
ecology.  So,  too,  is  the 
treatment  of  pollination 
(Chapter  VIII),  of  seed  dispersal  (Chapter  IX),  and  much 
of  the  chapter  on  Weeds.  The  relation  of  parasites  to  their 
hosts  and  of  symbionts  to  each  other  (Chapter  XXI)  consti- 
tutes a  most  important  part  of  ecological  botany.  In  the  cases 
here  referred  to,  however,  the  main  emphasis  was  laid  on  the 

1  See  Warming,  (Ecology  of  Plants  (Clarendon  Press,  Oxford) ;  Schimper, 
Plant  Geography  on  a  Physiological  Basis  (Clarendon  Press,  Oxford)  ;  and 
Coulter,  Barnes,  and  Cowles,  Textbook  of  Botany,  Part  II  (American  Book 
Company,  New  York). 

An  excellent  bibliography  of  the  subject  will  be  found  in  Warming's  work, 

477 


478 


PBACTICAL  BOTANY 


FIG.  358.  The  pond  lily,  an  aquatic  with  floating  leaves  and  submerged  stems 


FIG.  359.  Free-floating  aquatic  plants  in  a  pool 

Aquatics  with  aerial  leaves,  the  most  conspicuous  of  which  is  the  arrowhead 
(Sagittaria) ,  grow  in  the  mud  about  the  pool.   Photograph  by  Charles  Gordon, 


ECOLOGICAL  GROUPS  479 

structure  and  mode  of  activity  of  the  plant  or  organ  under 
discussion.  From  the  point  of  view  of  the  ecologist  the  prin- 
cipal things  to  be  considered  are  the  relations  (often  very 
intricate)  between  the  plant  and  other  plants  or  animals,  how 
the  plant  meets  the  conditions  of  soil  and  climate  under  which 
it  exists,  and  why  plants  are  distributed  in  the  various  regions 
of  the  earth's  surface  as  they  are. 

440.  Systematic  groups  not  ecological.    The  way  in  which 
plants  are  classified  according  to  their  relationships  has  already 
been  described  (Chapter  X).    The  systematic  grouping  into 
classes,  orders,  families,  and  so  on,  has  no  necessary  relation 
to  the  life  habits  of  the  plant.    The  Heath  order,  for  exam- 
ple, includes  ordinary  plants  with  the  capacity  for  photosyn- 
thesis (Fig.  299),  and  also  saprophytes  (Figs.  307  and  308). 
Some  of  its  members  are  sun-loving  plants  and  some  are  shade- 
enduring,  some  can  live  in  very  dry  soil  and  others  occur  only 
in  swamps.    One  familiar  genus  of  the  Morning-glory  family 
(Cuscuta,  Fig.  351)  is  parasitic,  while  most  of  the  genera  of 
this  family  get  their  living  in  the  ordinary  way,  from  air  and 
soil.   Several  genera  of  the  Figwort  family  (such  as  the  painted 
cup)  are  root  parasites,  while  most  are  not. 

441.  Ecological  groups.   In  classifying  plants  according  to 
their  ecological  relations  'they  are   generally  grouped  with 
regard  to  their  water  requirements,  as  follows: 

(1)  Water  plants,  those  which  usually  live  only  in  the  water1 
or  in  marsh  soil  saturated  with  water2;  they  may  be  unattached, 
like  many  algse  (Chapters  XII,  XIII)  and  duckweed  (Fig. 
357)  ;  or  rooted,  like  arrowhead  (Fig.  359),  cat-tails,  pickerel 
weed,  and  pond  lilies  (Figs.  55  and  358). 

(2)  Land  plants,  those  which  live  in  ordinary  soil  or  on 
rocks,  the  bark  of  trees,  and  so  on. 

The  two  main  ecological  divisions  of  land  plants  are  as 
follows  3 : 

(a)  Xerophytes,  plants  which  can  tolerate  extremely  dry 
conditions,  as  many  lichens  (Figs.  190-193),  cacti  (Fig.  68), 

1  Hydrophytes,  2  Helophytes.  8  For  halophytes  see  Sect.  452, 


480 


PRACTICAL  BOTANY 


and  in  general  plants  which  inhabit  exposed  or  excessively 
dry  regions. 

(6)  Mesophytes,  plants  which  require  a  moderate  amount 
of  moisture,  such  as  most  cultivated  plants  and  our  common- 
est deciduous  trees  and  shrubs. 


FIG.  360.  Cross  section  of  stem  of  pond- 
weed  (Potamogeton)  showing  air  passages 

a,  much  magnified.  After  Green 

442.  Characteristics  of  water  plants. 
Those  water  plants  which  live  wholly  sub- 
merged generally  differ  far  more  in  their 
form  and  structure  from  land  plants  than  do 
those  which  (like  many  grasses  and  sedges) 
grow  in  very  wet  soil.  From  the  situation  in 
which  they  grow,  submerged  plants  are  less 


>  3^1.  A  marsh 
Plant  (Limnophila) 


familiar  to  us  than  common  land  plants  ;    The  thread-like  low- 

*T  ,  er  leaves  are  water 

but    most    people    who    know    OUt-of-door     leaves.     There    are 


things  well,  have  seen  pondweeds,  water    -™at°' 
crowfoots,  bladderworts  (Fig.  362),  mare's-    ahove  the  middle, 

.    .,  -i    ,  7-17    7     N  /•    ,i         and  the  upper  ones 

tail,  water  weed  (Modea),  or  some  of  the    are  air  leaves.  About 
aquatic  mosses.    It  is  important  to  notice    one  half  natural  size. 

11  11  PI  i  After  Goebel 

how  thoroughly  most  ot  these  are  buoyed 
up  and  supported  by  the  water.    All  such  plants  are  soft  and 
limp,  without  the  distinct  tough  epidermis  of  land  plants,  and 
the  leaves  are  often  slender  or  thread-like. 


ECOLOGICAL  GKOUPS 


481 


Definitely  stated,  some  of  the  most  noticeable  characteristics 
often  found  in  submerged  aquatic  seed  plants  are  1 : 

(1)  Slight  development  of  the  root  system. 

(2)  Slight  development  of  wood  cells  and  vessels. 

(3)  Stiffening  structures  scanty  or  lacking. 

(4)  Air  spaces  large  and  abundant. 

(5)  The  epidermis  thin  and  the  cuticle  very  thin  or  wanting. 

(6)  The  leaves  often  dissected  into  thread-like  divisions. 
What  are  probable  reasons  for  character- 
istics (l)-(5)  ?   The  thread-like  divisions  of 

the  leaves  mentioned  in  (6)  are  thought  to 

favor  exchange  of  gases 

between   the  water  in 

which  they  are  dissolved 

and  the  leaf  interior  and 

to  offer  little  resistance 

to  currents  of  water. 

443.    Characteristics 
of   xerophytes.     There 

are  so  many  types   of       •FlG-  ^62>  A  free  branch  and  two  buds  °f 

,     .     .,  a  large,  common  bladderwort 

xerophytes    that   it    is 

...  ,       .  f  After  Beal 

not  possible  in  a  few 

words  to  sum  them  up  or  to  give  the  student  a  comprehensive 
idea  of  their  peculiarities  of  structure  and  of  function.  Per- 
haps the  easiest  way  to  suggest  the  leading  characteristics  of 
the  group  is  to  mention  a  few  familiar  representatives  of  the 
leading  types  as  follows : 

(1)  The  olive  (Fig.  51),  the  rubber  tree  (Ficus  elasticci), 
and  the  wax  plant  (Hoya),  not  uncommon  in  greenhouses,  are 
good  examples  of  xerophytes  with  hard,  thick-skinned  leaves, 
which  have  a  compact  interior  parenchyma,  without  the  abun- 
dant air  spaces  shown  in  Fig.  11. 

1  The  student  must  not  think  of  these  characteristics  as  abnormal  and 
of  those  of  ordinary  land  plants  as  normal.  It  is  possible  that  the  earliest 
plants  were  aquatics  and  that  the  aquatics  of  to-day  are  more  like  primitive 
plants.  But  it  is  better  to  leave  such  reasoning  for  more  advanced  studies. 


482 


PEACTICAL  BOTANY 


(2)  The  various  kinds  of  heather,  knotgrass  (Polygonum 
aviculare),  knawel  (Scleranthus  annuus),  and  the  rushes  are 
instances  of  xerophytes  with  small  leaves,  exposing  compara- 
tively little  surface  to  the  sun  and  air. 

(3)  Century  plants  (Fig.  62),  houseleeks,  and  aloes  are 
good  examples  of  fleshy-leaved  xerophytes. 

(4)  Many  xerophytes  combine  in  their  leaves  some  of  the 
characteristics  of  groups   (1),  (2),  and  (3).    The  leaves   of 
cedars,  hemlocks,  firs,  and  spruces  have  a  thick  epidermis  and 

close  interior  struc- 
ture, like  that  shown  in 
Fig.  249,  and  are  also 
small,  exposing  little 
surface.  The  common 
purslane,  the  portu- 
laca,  and  the  ice  plants 
(Mesembryanthemum) 
have  small  and  rather 
fleshy  leaves. 

Many  xerophytes 
have  extraordinarily 
developed  root  systems,  as  in  the  case  of  the  mesquite  (Seel;. 
27),  and  so  can  draw  moisture  from  great  depths  in  the  earth. 
Others  have  extensive  provisions  for  water  storage  (Sects.  34, 
66,  67).  Among  these  the  cacti  are  notable  for  the  amount 
of  water  which  they  can  store  in  their  succulent  stems,  which 
are  often  fluted,  so  as  to  expand  and  contract  readily.  This 
water  has  been  rapidly  absorbed  by  the  spreading,  shallow 
root  system  from  the  layer  of  earth  (only  an  inch  or  two 
deep),  which  is  moistened  by  the  rare  rains  of  the  desert  re- 
gions where  many  such  cacti  grow.  Between  rains  the  roots 
of  these  cacti  serve  only  for  anchorage. 

Xerophytes  in  general  are  so  constituted  as  to  transpire 
little  at  any  time,  or  else  to  be  able,  in  case  of  danger  from 
excessive  dryness,  to  reduce  the  amount  of  transpiration  to  a 
very  low  value. 


FIG.  363.   Cross  section  of  rolled-up  leaf  of 
crowberry  (Empetrum  nigrum) 

Magnified 


ECOLOGICAL  GROUPS 


483 


In  order  to  realize  the  extreme  danger  to  which  plants  are 
exposed  from  dryness,  one  needs  only  to  remember  how  often 
harvests  in  great  part  fail  from  the  effects  of  drought.  This 
may  mean  that  the  entire  plants  have  been  killed,  or  only  that 
they  have  not  borne  much  fruit  or  seed,  or  that  the  roots,  stems, 
or  leaves  are  stunted.  Many  wild  plants  are  as  sensitive  to 
prolonged  drought  as  are  ordinary  field  crops,  and  irrigation 
of  a  desert  region  which  has  a 
rich  soil  helps  the  growth  of 
weeds  as  much  as  it  does  that 
of  the  crops  among  which  they 
spring  up. 

444.  Means  of  limiting 
transpiration.  Some  of  the 
principal  means  of  limiting 
transpiration  are  as  follows l : 

(1)  Compact  arrangement 
of  the  parenchyma  cells  in  the 
interior  of  the  leaf. 

(2)  Development   of   a 
thick-walled  epidermis  (Figs. 
249  and  364). 

(3)  Situation   of  the   sto- 
mata  in  pits  or  furrows  (Figs. 
249  and  364). 

(4)  Inclosing  the  stomata 
in   a  sort  of   tubular  cavity 

formed  by  the  curving-in  of  the  margins  of  the  leaf  (Fig.  363). 

(5)  Presence  of  a  coating  of  dead  hairs,  filled  with  air,  on 
one  or  both  surfaces  of  the  leaf  (Fig.  57). 

(6)  Temporary  reduction  of  the  evaporating  surface,  as 
by  rolling  up  leaves  (Fig.  2),  shedding  leaves,  reduction  of 
living  parts  to  a  buried  root,  bulb,  tuber,  rootstock,  or  some 
combination  of  thickened  roots  and  underground  stems. 

1  The  subject  is  a  very  extensive  one,  fully  treated  in  the  writings  of 
Warming,  Schimper,  Goebel,  Volkens,  and  other  ecologists. 


FIG.  364.  Waterproof  epidermis  and 
protected  stoma  of  the  century  plant 

c,  cuticle ;  cu,  cutinized  (waterproofed) 
layer  of  epidermis;  ce,  cellulose  layer 
of  epidermis ;  pi,  pit,  at  the  bottom  of 
which  the  stoma  is  situated;  po,  pore 
of  the  stoma.  Magnified  about  220 
diameters.  After  Luerssen 


484 


PRACTICAL  BOTANY 


(7)  Reduction  of  leaf  surface,  as  in  the  case  of  needle-shaped 
(Fig.  248),  scale-like,  or  other  small,  narrow  kinds  of  leaf. 

(8)  Partial  or  complete  absence  of  useful  leaves,  as  in  the 

"  switch  plants,"  such 
as  Spartium,  Casuarina 
(Fig.  365),  and  so  on ; 
and  iii  asparagus,  the 
cacti  (Fig.  65),  and 
some  euphorbias  (Fig. 
366). 

445.  Discussion  of 
xerophytic  characters. 
The  first  four  kinds  of 
characters  operate,  as 
may  be  readily  under- 
stood, greatly  to  limit 
the  loss  of  water.  Close- 
ly packed  parenchyma 
cells  in  the  leaf  interior, 
with  few  air  spaces, 
give  little  opportunity 
for  the  water  in  the 
interior  cells  to  escape 
into  the  internal  atmos- 
phere of  the  leaf  and  so 
gradually  pass  off  into 
the  air.  When  the  epi- 
dermis is  thick,  espe- 
cially if  it  is  covered 
with  a  heavy,  water- 
proof cutinized  layer 
(cu,  Fig.  364),  transpi- 
ration when  the  stomata  are  closed  is  very  scanty.  Stomata 
situated  at  the  bottoms  of  microscopic  pits  or  furrows  are 
much  protected  from  drafts  of  air  and  therefore  give  off  vapor 
slowly.  And  when  the  stomata-bearing  leaf  surface,  as  in  the 


FIG.  365.  Casuarina,  an  Australian  switch 
plant  destitute  of  foliage  leaves  and  depend- 
ing on  the  chlorophyll-containing  cells  of  the 

bark  for  photosynthesis 
Photograph  by  Robert  Cameron 


ECOLOGICAL  GROUPS  485 

crowberry  (Fig.  363),  forms  the  interior  of   a  nearly  closed 
tube,  transpiration  is  still  more  hindered. 

Hairy  leaves  (5)  are  characteristic  of  plants  of  dry  climates, 
as  the  Mediterranean  region,  and  of  dry  exposed  areas  like 


FIG.  366.  Part  of  a  euphorbia  stem,  the  branches  showing  considerable 
resemblance  to  those  of  some  cacti 

the  higher  portions  of  the  great  Western  plains  in  this  country. 
Generally  the  hairs  are  relatively  simple  in  their  structure 
and  do  not  completely  cover  the  surface.  But  in  many  in- 
stances the  hairs  assume  shield-like  or  other  flattened  forms, 
and  they  may  overlap  so  as  more  than  to  cover  the  surface 


486  PRACTICAL  BOTANY 

on  which  they  occur  most  abundantly  (usually  the  lower 
one,  Fig.  57,  A).  The  same  species  or  individual  sometimes 
becomes  more  hairy  when  subjected  to  a  drier  atmosphere. 
Experiments  show  that  shearing  off  the  hairs  from  the  surface 
of  the  living  leaf  increases  the  loss  of  water  by  transpiration, 
sometimes  even  doubling  its  amount. 

Rolled-up  leaves  (6)  are  familiar  in  the  case  of  corn  (Fig.  2). 
It  would  not  be  easy  to  perform  a  field  experiment  to  prove 
exactly  how  much  the  loss  of  water  is  lessened  in  the  rolled 
corn  leaves,  but  it  would  seem  that  the  surfaces  are  considr 
erably  less  freely  exposed  to  the  air  in  the  roiled  condition 
than  when  the  blades  are  flat,  and  free  exposure  is  a  well- 
known  factor  in  increasing  transpiration.  In  some  xerophytic 
grasses  there  is  a  complicated  arrangement  of  folds  in  the 
leaves  by  means  of  which  they  can  close  up  the  transpir- 
ing surface  (almost  as  in  Fig.  363)  or  open  it  completely  to 
the  air. 

Shedding  the  leaves  (6)  is  the  principal  means  by  which  our 
deciduous  trees  and  shrubs  escape  the  dangers  of  dry  winter 
weather  when  no  moisture  can  be  absorbed  from  the  ground. 
It  has  been  found  that  the  larch  (which  sheds  its  leaves)  is 
more  resistant  to  such  conditions  than  are  most  of  the  ever- 
green conifers.  Some  shrubs  retain  or  shed  their  leaves  in 
a  rainless  summer  according  to  the  amount  of  soil  mois- 
ture with  which  they  are  supplied.  The  Euphorbia  splendens 
(Fig.  292,  A)  is  a  commonly  cultivated  plant  which  well  illus- 
trates this  capacity  to  adjust  the  amount  of  leaf  surface  to 
a  varying  moisture  supply. 

Plants  with  bulbs  (6)  are  notably  common  in  regions  where 
there  is  a  long  rainless  summer.  To  a  botanist  one  of  the 
most  interesting  sights  of  the  Mediterranean  coast  region  is 
the  sudden  blooming  of  many  bulb-bearing  plants  toward  the 
close  of  the  summer.  Most  conspicuous  of  these  is  a  mem- 
ber of  the  Lily  family,  Urginea  Scilla,  which  sends  up  its  stout 
flower  stalk,  almost  as  tall  as  a  man,  out  of  the  earth  baked 
hard  by  two  or  more  months  of  hot  weather  almost  without 


ECOLOGICAL  GROUPS  487 

rain.  Since  there  are  no  living  leaves  at  the  base  of  the  flower 
stalk  it  has  the  curious  appearance  of  a  blooming  stem  stuck 
upright  in  dry  earth. 

Absolutely  leafless  plants  (8)  are  not  very  numerous,  but 
there  are  plants,  like  the  common  asparagus  and  most  cacti, 
which  have  very  small  and  short-lived  leaves  that  are  often 
nearly  or  quite  functionless.  In  the  common  garden  asparagus 
these  may  be  seen  as  triangular  scales  on  the  fleshy  shoots 
sent  up  in  early  spring.  The  green,  bristle-like  growths  on 
the  main  branches  of  asparagus  plants  throughout  the  summer 
perform  the  offices  of  leaves  but  are  stem-like  in  their  origin. 
In  the  cacti  the  leaves  often  appear  as  awl-shaped,  or  rather 
stout,  bristle-like  organs,  borne  at  the  nodes,  which  soon 
wither  and  fall.  In  such  plants  the  photosynthetic  work  all 
the  year  round  is  done  by  chlorophyll-bearing  cells  close  under 
the  epidermis  of  the  stem.  In  some  switch  plants  a  crop  of 
small  leaves,  borne  only  during  two  or  three  months  of  early 
spring,  perform  active  photosynthesis  while  they  last. 

446.  Characteristics  of  mesophytes.  Since  mesophytes  do 
not  live  under  such  conditions  as  frequently  to  run  the  risk 
either  of  drowning  or  of  drying  up,  they  do  not,  as  a  rule, 
show  extraordinary  modifications  of  structure,  such  as  would 
enable  them  to  carry  on  exchange  of  gases  under  water  or 
to  prevent  excessive  transpiration  in  dangerously  dry  air.  A 
large  part  of  what  has  been  said  in  the  preceding  chapters 
about  the  structure  and.  functions  of  seed  plants  has  had 
reference  to  mesophytes,  —  the  average  plants,  —  and  it  is 
therefore  unnecessary  in  this  place  to  go  into  details  in  regard 
to  their  characteristics.  In  many  respects  these  are  midway 
between  the  characteristics  of  water  plants  and  those  of  ex- 
treme xerophytes.  In  order  to  fix  his  knowledge  of  the  sub- 
ject, the  student,  after  doing  what  laboratory  and  field  work 
he  can  upon  the  ecological  groups  discussed  in  Sects.  440- 
446,  should  summarize  his  impressions  by  comparing  three 
or  more  plants,  each  typical  of  one  of  the  groups,  in  tabular 
form  somewhat  as  follows : 


488 


PRACTICAL  BOTANY 


A  rooted  hydrophyte 
(water  milfoil  or 
mare's-tail  l) 

A  mesophyte 
(the  common  bean  l) 

A  xerophyte 
(the  houseleek  l) 

Root  system 

General  form 
of  stem 

Relative     amount 
of  development  of 
wood  cells  in  stem 

Relative    develop- 
ment of  vessels  in 
stem 

Development  of  ai  r 
passages  in  stem 

General  form  of 
leaves 

Water  storage   in 
leaves 

• 

Epidermis  and 
cuticle 

Stomata 

Length     of     time 
plants  can  remain 
alive  in  air  of  room 
with  roots  in  soil 
that  is  not  watered 

1  These  plants  are  merely  suggested.  Pondweed  (Potamogetori),  water 
weed  (Elodea),  or  one  of  the  species  of  Banunculus  with  submerged,  dis- 
sected leaves,  will  answer  well  as  representative  aquatics.  There  are  hun- 
dreds of  mesophytes  from  which  to  choose.  Century  plants  (Agave),  cacti, 
aloes,  or  echeverias  are  good  examples  of  xerophytes. 


ECOLOGICAL  GROUPS 


489 


Make  a  list  of  all  the  aquatic  seed  plants  that  you  know, 
of  some  of  the  principal  marsh  plants,  of  several  herbaceous 
and  several  woody  mesophytes,  of  all  the  xerophytes  you  know, 
—  the  xerophytes  arranged  somewhat  in  the  order  of  their 
capacity  to  resist  drought  conditions. 

447.  Ecological  groups  based  on  light  relations.  Plants 
which  prepare  their  food  by  photosynthesis  evidently  need 


FIG.  367.    Spanish  moss  (Tillandsia) 
growing  on  branches  of  a  tree 

Much  reduced.  Photograph  by 
S.  M.  Tracy 


FIG.  368.  Tufts  of  Spanish  moss,  with 
leaves  of  the  magnolia  on  which  it  grew 

Reduced.  Photograph  by  Florida  Agri- 
cultural Experiment  Station 


light  as  much  as  they  do  air  or  water;  but  there  is  great 
diversity  in  their  demands  as  regards  intensity  of  light.  The 
practical  forester  soon  becomes  familiar  with  this  fact,  and 
the  gardener  and  floriculturist  know  that  while  some  plants, 
such  as  tulips,  poppies,  verbenas,  and  most  composites,  need 
all  the  sun  they  can  get,  other  plants,  as  most  ferns,  lilies  of 
the  valley,  spiderworts,  many  violets,  many  genera  of  the  Pars- 
ley family  and  the  Heath  family,  grow  best  in  partial  shade. 


490 


PKACTICAL  BOTANY 


The  various  strata  or  stories  of  vegetation  in  a  forest  are 
usually  arranged  somewhat  in  the  order  of  their  light  require- 
ments, the  plants  most  tolerant  of  shade  at  the  bottom  and 
the  most  intolerant  species  at  the  top.  Thus  in  an  open 
forest  composed  mainly  of  white  pines  mixed  with  a  few 

other    conifers    and    some 

deciduous  trees,  in  New 
England,  we  may  find  some 
such  assemblage  as  this: 
close  to  the  ground  vari- 
ous species  of  mosses,  the 
most  conspicuous  being  the 
pigeon-wheat  moss  (Polyt- 
richum).  Rising  but  little 
above  the  mosses  are  one 
or  two  species  of  "  ground 
pine,"  or  "Christmas  ever- 
green" (Lycopodium,  Fig. 
245).  Mingled  with  these 
are  many  herbaceous  spe- 
cies, or  very  small  under-, 
shrubs  representing  the 

seed  plants,  all  shade-loving 
FIG.  369.  An  air  plant  ( TWandsia)  of  the  .        guch  M  rattlesnake 

Pineapple  family  „    , 

plantain,1  "  wild  lily  of  the 

Living  as  an  epiphyte,  but  having  numerous  r  i  i          • 

roots,  it  is  intermediate  in  habit  between  valley,    2    chickweed,    Wlll- 

the  common  pineapple  (Fig.  283),  which  tergreen  3  common  wood 
grows  rooted  in  the  earth,  and  the  Spanish  &  .  .  9  . 

moss  (Fig.  368),  which  is  rootless  and  hangs  SOrrel,4  prince  S  pine,0  Shin- 

suspended  from  the  bark  of  trees.  Photo-  |eaf  6  partridge  berrv,7  and 
graph  by  Robert  Cameron  ^  Q     *  .< 

rattlesnake-weed.8     Above 

these,  if  the  woods  are  young,  grow  such  larger  shrubs  and 
small  trees  as  Juneberry,9  blueberry,10  and  gray  birch.11  Mixed 
with  these  are  young  spruces  and  perhaps  hemlocks.  Only 

1  Goody  era.         2  Maianihemum.         8  Trientalis.         4  Oxalis  Acetosella. 

6  Chimaphila.       6  Pyrola.       7  Mitchella.       8  Hieracium.       9  Amelanchier. 

10  Vaccinium  vacillans.        ll  Betula  populifolia- 


ECOLOGICAL  GROUPS  491 

the  tall  pines  which  overtop  all  the  other  trees  receive  the 
sunlight  in  its  full  intensity ;  under  the  densest  shade  of  the 
pines  the  illumination,  compared  with  that  of  the  unshaded 
tree  tops,  may  be  only  one  fiftieth  or  less.1 

In  a  forest  the  number  and  character  of  the  strata  of  vege- 
tation depend  largely  upon  the  kinds  and  density  of  the  trees 
that  compose  the  uppermost  stratum.  In  an  average  deciduous 
forest  such  as  is  often  found  throughout  the  Central  States 
the  uppermost  stratum  consists  of  trees  such  as  oaks,  maple, 
beech,  elm,  hickory,  and  tulip  (Fig.  319).  In  some  regions 
one  finds  an  almost  pure  beech  or  maple  forest.  The  oak- 
maple  or  oak-maple-beech  combination  is  not  uncommon.  If 
these  trees  grow  closely  crowded,  the  shade  underneath  is  very 
dense  and  few  shorter  trees  or  shrubs  are  found.  When  the 
forest  is  more  open  a  second  stratum  of  young  trees  and  tall 
shrubs  is  found.  This  stratum,  in  addition  to  the  young  trees, 
may  contain  the  bladderwort  (Stapliylea),  the  hop  hornbeam 
(Ostrya),  the  ironwood  (Carpinus),  and  many  others.  There 
may  be  a  stratum  of  lower  shrubs  immediately  below  the  tall- 
shrub  stratum,  and  this  lower-shrub  stratum  often  is  charac- 
terized by  the  blackberry,  raspberry,  and  the  greenbrier  or  cat 
claw.  The  next  stratum  usually  is  characterized  by  many  tall 
ferns  and  many  kinds  of  flowering  plants  that  thrive  in  deep 
shade.  Below  the  ferns  and  upon  the  soil  or  decaying  vegeta- 
tion is  the  lowest  stratum,  which  may  include  many  kinds  of 
toadstools  and  mushrooms  and  other  fungi,  mosses  of  many 
kinds,  occasionally  some  of  the  leafy  liverworts,  and  some  of 
the  soil  lichens.  In  some  forests  in  which  there  are  but  few 
strata  of  vegetation,  during  the  greater  part  of  the  growing 
season  the  tall  trees  constitute  almost  the  entire  conspicuous 
flora.  In  early  spring,  however,  such  forests  usually  have  a 
low  stratum  of  early -flowering  plants  (spring  beauty,  blood- 
root,  dogtooth  violet  or  deer's-tongue,  Dutchman's-breeches, 
etc.),  which  for  a  brief  period  carpet  the  forest  floor.  These 

1  In  the  pine  forests  of  the  Tyrol,  Wiesner  found  the  illumination  in 
entire  shade  only  one  sixtieth  to  one  ninetieth  of  full  sunlight. 


492  PRACTICAL  BOTANY 

plants  flower  at  the  expense  of  food  material  that  was 
deposited  in  former  seasons  (Sects.  34  and  69),  and  do  most 
of  their  vegetative  work  before  the  leaves  of  the  trees  are 
developed  so  as  to  shade  them.  As  the  season  advances 
and  the  light  intensity  increases,  these  low  plants  may  still 
work  by  means  of  the  diffuse  light  that  is  filtered  through 
the  tree  tops. 

Any  local  forested  area  will  afford  students  interesting 
studies  in  the  strata  of  forest  vegetation. 

448.  Fractional  part  of  total  sunlight  required  by  various 
plants.1  The  proportion  of  the  full  strength  of  sunlight  re- 
quired by  any  given  species  is  not  the  same  in  different  lati- 
tudes ;  for  example,  the  common  dandelion  at  Vienna  (lat. 
48.12°)  may  grow  in  an  illumination  of  one  twelfth,  but  in 
northern  Norway  (lat.  70.33°)  the  total  light  of  the  sun  is 
needed  to  enable  it  to  grow. 

The  same  individual  often  requires  different  amounts  of 
light  during  different  stages  of  its  development.  The  English 
ivy  (Hedera)  will  not  bloom  with  a  light  intensity  less  than 
two  ninths  of  total  daylight,  and  therefore  flowers  are  never 
seen  on  ivies  grown  as  house  plants.  But  the  vegetative 
organs  continue  to  grow  with  an  illumination  as  low  as  one 
forty-eighth. 

Among  the  seed  plants  which  can  flourish  in  deep  shade 
are  many  species  of  epiphytes  and  lianas.  Good  examples  of 
the  former  are  many  tropical  orchids ;  of  the  latter,  one  of  the 
most  familiar  is  the  common  frost  grape  (Vitis  cor dif olio), 
which  can  grow  with  an  illumination  as  low  as  one  seventieth. 
On  the  other  hand,  plants  which  live  in  the  open  and  compara- 
tively unshaded,  like  all  the  larger  prairie  species,  such  as  many 
kinds  of  Liatris,  Coreopsis,  sunflowers,  rosinweeds,  some  iron- 
weeds  and  wormwoods,  require  high  illuminations  to  thrive. 

1  See  Wiesner,  Der  Lichtgenuss  derPflanzen  (Engelmann,  Leipzig).  Great 
caution  must  be  used  in  drawing  conclusions  on  this  head,  since  lack  of  soil 
water  and  salts  may  easily  be  responsible  for  part  of  the  effects  attributed  to 
scanty  light  supply. 


ECOLOGICAL  GKOUPS  493 

449.  Practical  applications  of  the  knowledge  of  light  require- 
ments. A  few  words  have  already  been  said  (Sect.  370)  about 
the  importance  of  recognizing  the  difference  in  the  light  re- 
quirement of  trees.  The  farmer  and  the  horticulturist  often 
have  need  of  considering  the  light  requirements  of  cultivated 
plants.  It  is  not  infrequently  desirable  to  grow  some  kind  of 
crop  in  partial  shade,  as  in  a  young  orchard.  In  such  situa- 
tions some  of  the  plants  which  bear  small  fruits,  as  raspberries, 
blackberries,1  and  strawberries,  will  succeed  fairly  well.  So 
also  will  common  beans  and  broad  or  horse  beans.  Pumpkins 
and  squashes  grow  well  in  cornfields.  A  good  many  useful 
grasses  are  tolerant  of  shade,  and  mixtures  of  grass  seed  suit- 
able for  lawns  under  shade  trees  are  sold  by  the  principal 
seedsmen.  Some  of  the  grasses  of  more  or  less  value  for 
pasture  or  hay,  which  grow  in  moderate  shade,  are  Kentucky 
blue  grass,2  Canada  blue  grass,3  orchard  grass,4  rough-stalked 
meadow  grass,5  wood  meadow  grass,6  crested  dog's-tail,7  and 
sheep's  fescue.8 

Some  crops,  as  sugar  beets,  are  of  inferior  quality  when 
grown  in  partial  shade.  In  Austria-Hungary  the  beets  grown 
in  the  sun  were  found  by  one  observer  to  average  rather  more 
than  three  times  the  weight  of  those  grown  in  the  shade.  Add 
to  this  the  fact  that  the  sun-grown  beets  contained  about 
1J  per  cent  more  sugar  than  the  shade-grown  ones,  and  the 
importance  of  full  sunlight  for  the  sugar-beet  crop  becomes 
very  apparent.  Certain  crops  depend  for  complete  success 
upon  a  long  series  of  days  of  the  most  brilliant  sunshine. 

1  The  amount  of  shade  which  can  be  tolerated  by  plants  of  the  same 
genus,  natives  of  the  same  region,  often  differs  widely.    The  black  raspberry 
(Rubus  occidentalis)  has  been  found  to  flower  freely  but  to  mature  hardly 
any  fruit  in  a  situation  where  the  bushes  were  so  shaded  that  during  the 
earlier  half  of  the  day  they  received  but  one  twelfth  to  one  fifteenth  of  the 
total  sunlight,  although  they  had  full  sunlight  during  most  of  the  after- 
noon.  Mixed  with  these  bushes  were  blackberries  (perhaps  a  cultivated 
form  of  R.  allegheniensis)  which  flowered  and  fruited  abundantly. 

2  Poa  pratensis.         8  Poa  compressa.         4  Dactylis  glomerata.         *  Poa 
trivialis.       6  Poa  nemoralis.       7  Cynosurus  cristatus.       8  Festuca  omna. 


494  PRACTICAL  BOTANY 

Corn  is  one  of  the  most  important  of  these  crops,  and  the 
supremacy  of  the  corn  belt  in  the  United  States  is  perhaps 
as  much  due  to  the  amount  and  intensity  of  its  sunshine 
during  the  summer  months  as  to  its  admirable  soil.1 

In  planting  many  kinds  of  crops  (corn  among  others),  atten- 
tion should  be  given  to  allowing  light  to  enter  freely  between 
the  plants ;  otherwise  the  quantity  and  quality  of  the  product 
from  the  field  will  suffer.  Fruit  trees  should  be  pruned  so 
that  the  lower  limbs  will  not  be  prevented  from  developing 
by  the  shade,  and  should  be  planted  far  enough  apart  to  pre- 
vent injury  to  the  entire  tree  from  the  same  cause.  The  in- 
tensity of  sunlight  in  an  orchard  region  has  much  to  do  with 
the  amount  of  pruning  necessary  to  make  apple  trees  bear 
well-developed  and  ripened  fruit.  In  the  northeastern  states 
the  tops  of  the  trees  should  be  thinned  out  to  not  more  than 
half  the  thickness  allowable  in  the  Middle  West.  The  high 
color  of  apples  from  Colorado  and  other  regions  of  intense 
sunlight  is  due  to  this  abundant  light  supply,  which  brings 
about  the  coloration  even  in  trees  with  dense  tops. 

450.  Plant  distribution.2  The  subject  of  the  distribution  of 
plants  on  the  earth's  surface  was  at  first  discussed  almost 
wholly  as  a  group  of  geographical  facts.  While  travelers  for 
thousands  of  years  have  known  something  of  the  diversity  of 
the  vegetation  of  the  earth,  it  is  only  recently  that  careful 
attention  has  been  given  to  the  factors  which  determine  the 
kinds  of  plant  inhabitants  of  any  given  region. 

The  vegetation  of  any  portion  of  the  earth  is  usually  con- 
sidered either  from  the  floristic  or  the  ecological  point  of  view. 
In  the  former  case  the  student  takes  into  account  mainly  the 
kinds  of  plants  —  that  is,  the  species,  genera,  families,  and 

1  See  Warren,  Elements  of  Agriculture,  chap.  vii.   The  Macmillan  Com- 
pany, New  York. 

2  Within  the  limits  of  a  chapter  like  the  present  one  this  subject  can  only 
be  touched  upon.    Much  information  can  be  found  in  the  larger  physical 
geographies,  in  Schimper's  Plant  Geography  on  a  Physiological  Basis  (see 
p.  477),  and  in  the  popular  writings  of  naturalists  like  Humboldt,  Darwin, 
J.  D.  Hooker,  Wallace,  Belt,  Bates,  Hudson,  and  others. 


REGIONAL  DISTRIBUTION  495 

higher  groups  —  with  which  the  region  is  covered.  In  the 
latter  case  the  student  considers  mainly  the  ecological  groups 
which  are  present;  that  is,  whether  the  plants  are  water  or 
land  forms,  and  in  regard  to  the  land  plants  whether  they  are 
xerophytes  or  mesophytes.  In  studying  plant  distribution 
from  the  floristic  side  a  very  important  topic  is  the  considera- 
tion of  the  history  of  the  flora.  This  deals,  for  instance,  with 
such  questions  as  the  investigation  of  the  center  or  centers 
from  which  the  plants  were  derived,  the  course  which  they 
took  in  migrating  outward  from  those  centers,  and  the  time 
required  to  cover  the  territory  which  they  now  occupy. 

451.  Ecological  plant  geography.  For  most  purposes  the 
ecological  characters  of  the  principal  floras  of  the  earth  are 
more  important  than  their  systematic  relations;  that  is,  we 
are  especially  concerned  to  know  that  arctic  vegetation  is 
scanty  and  of  dwarf  forms,  that  vast  grassy  meadows  and 
prairies  and  extensive  hard-wood  forests,  often  of  few  spe- 
cies, are  characteristic  of  temperate  regions,  and  that  tropical 
forests  (in  the  rainy  areas)  are  extremely  dense,  interwoven 
with  lianas,  and  burdened  with  epiphytes.  Such  facts  are  of 
more  general  interest  than  the  knowledge  of  the  proportion 
of  the  floras  of  the  different  zones  constituted  by  each  family 
represented. 

The  most  important  unit  for  beginners  in  ecological  plant 
geography  to  consider  is  the  association.^-  In  order  to  see  what 
this  term  means  it  will  be  necessary  to  recall  some  of  the 
things  which  most  observing  people  already  know  without 
having  studied  botany.  In  a  pond  like  that  shown  in  Fig.  358 
one  is  likely  to  find  white  pond  lilies,  yellow  pond  lilies,  pick- 
erel weed,  arrowhead,  pondweed  (Potamogetori),  water  smart- 
weeds,  rushes,  and  perhaps  a  good  many  other  flowering  plants. 
Besides  these  there  may  be  dozens  of  species  of  blue-green 

1  The  plant  formation  is  a  larger  unit,  made  up  of  associations.  Forma- 
tions may  consist  of  many  families,  genera,  and  species,  but  must  comprise 
such  vegetation  forms  as  are  able  to  thrive  in  the  habitat  where  the  forma- 
tion occurs. 


496 


PRACTICAL  BOTANY 


and  green  algae.  Coniferous  or  hard-wood  forests  (Sect.  446) 
contain  varied  assemblages  of  herbs,  shrubs,  and  trees.  The 
plant  life  of  the  pond  and  that  of  the  forest  are  good  examples 
of  associations.  A  plant  association  is  a  set  of  plants,  usually  con- 
sisting of  several  genera  (perhaps  comprising  many  species),  of 
somewhat  similar  aspect,  living  together  under  essentially  simi- 
lar conditions.  It  is  important  to  notice  that  even  a  small  area 


FIG.  370.  A  flowerless  xerophyte  (the  lichen  Usned)  growing  on  conifers 
in  the  Maine  woods 

may  contain  several  associations.  For  instance,  a  rocky  ledge 
in  a  meadow  may  have  an  entirely  different  plant  population 
from  that  of  the  meadow  around  it.  The  aspect  of  an  associa- 
tion depends  largely  upon  the  kind  of  vegetation  forms  (hy- 
drophytes, mesophytes,  or  xerophytes)  which  the  station  can 
support.  It  is  also  influenced  by  other  circumstances,  such  as, 
in  the  case  of  aquatics,  whether  the  plants  are  wholly  or  only 
partially  submerged ;  in  the  case  of  land  plants,  whether  trees, 
shrubs,  or  herbs  predominate. 


REGIONAL  DISTRIBUTION 


497 


452.  What  determines  the  occurrence  of  vegetation  forms. 
The  ecological  type  of  the  plants  which  inhabit  any  kind  of 
habitat  depends  usually  on  its  soil  (in  the  case  of  aquatics, 
the  water),  its  climate,  or  both.  If  we  find  a  region  with 


FIG.  371.  Mangroves,  halophytes  with  aerial  roots 

The  young  seedlings  are  rooting  in  the  beach  sand  and  the  thicket  is 
gradually  pushing  out  toward  the  sea 

decidedly  xerophytic  vegetation,  this  fact  may  be  due  to  any 
one  of  several  causes,  as  follows : 

(1)  A  climate  with  very  little  annual  rainfall. 

(2)  A  climate  with  considerable  rainfall  during  the  year 
but  with  long  rainless  periods. 


498  PEACTICAL  BOTANY 

(3)  A  soil  or  other  root  foothold  which  does  not  retain  water, 
such  as  dry  sand,  bare  rock  surfaces,  or  the  bark  of  trees. 

(4)  A  soil  which  contains  a  good  deal  of  water,  but  is 
physiologically  dry,  —  that  is,  does  not  yield  water  freely  for 
absorption  by  the  roots. 

As  regards  (1)  and  (2),  it  is  easy  to  see  that  regions  like 
some  of  the  Arizona  deserts,  with  only  about  a  half  inch  of 
rain  during  the  entire  year,  can  hardly  support  any  perennial 
seed  plants  other  than  extreme  xerophytes.  Countries  like 
those  which  border  portions  of  the  Mediterranean,  with  a 
total  rainfall  for  the  year  of  30  to  40  inches,  but  one  which 
for  four  months  of  summer  sometimes  falls  as  low  as  one 
half  inch,  with  a  maximum  daily  summer  temperature  in  the 
sun  of  130  °  F.  and  an  intensely  dry  atmosphere,  are  better 
suited  to  support  xerophytes  than  mesophytes. 

A  plant  under  the  conditions  mentioned  in  (3)  may  be  del- 
uged by  violent  rains  during  much  of  the  year  and  yet  in  a  few 
hours  after  each  rain  be  wholly  cut  off  from  any  water  supply. 
Most  lichens  (Figs.  190-193  and  370)  and  many  tropical  epi- 
phytic seed  plants  (Fig.  20),  as  well  as  our  own  Spanish  moss 
(Figs.  367  and  368),  live  under  such  conditions  as  these. 

It  is  difficult  at  first  sight  to  recognize  what  is  meant  by 
physiologically  dry  soils,  such  as  are  mentioned  in  (4).  Ordi- 
narily water  cannot  be  absorbed  from  soils  below  a  certain 
temperature,  which  varies  in  different  kinds  of  plants.  Hence 
soils  in  a  frozen  or  nearly  frozen  condition  are  physiologically 
dry,  although  much  water  may  be  present  in  the  form  of  ice. 
Soils  (or  waters)  containing  much  of  the  humous  acids  derived 
from  decaying  vegetation  are  perhaps  not  physiologically  dry, 
but  the  acids  which  they  contain  are  injurious  to  most  plants 
and  it  is  necessary  that  species  which  are  found  in  such  sit- 
uations shall  be  able  to  live  without  absorbing  much  water. 
Hence  many  marsh  plants,  rooted  in  very  wet  mud,  have  xero- 
phytic  leaves.  Finally,  soils  containing  much  saline  matter1  are 

1  As  common  salt,  magnesium  chloride,  sodium  carbonate,  sodium  sul- 
phate, magnesium  sulphate,  or  mixtures  of  these  salts. 


REGIONAL  DISTRIBUTION 


499 


physiologically  dry.  On  such  soils  the  vegetation  is  composed 
of  halophytes,  or  plants  which  tolerate  a  larger  proportion  of' 
mineral  salts  in  the  soil  than  can  be  endured  by  most  plants.1 
One  of  the  best-known  halophytes  is  the  common  garden 
asparagus,  which  sometimes  has  its  growth  increased  by  the 
addition  of  common  salt  to  the  soil  in  which  it  is  growing. 


FIG.  372.  Plants  taking  possession  of  recently  formed  islands  in  a  river 
Along  the  bank  at  the  right  are  three  zones  of  woody  plants 

In  many  points  of  form  and  structure  halophytes  usually 
resemble  ordinary  xerophytes,  and  many  of  them  are  fleshy- 
stemmed  or  fleshy-leaved.  Such  plants  abound  in  the  salt 
marshes  of  the  Atlantic  coast  and  in  some  of  the  "  alkali " 
tracts  of  the  extreme  Southwest. 

1  For  example,  young  seedlings  of  the  saltwort  (Salsola  Kali,  var.  tenui- 
folia),  a  typical  halophyte,  live  longer  in  a  5.5  per  cent  solution  of  common 
salt  than  most  herbaceous  mesophytes  can  in  a  1.5  per  cent  solution.  In 
other  words,  the  tolerance  of  Salsola  for  common  salt  is  at  least  four  times 
as  great  as  that  of  most  herbs. 


500 


PRACTICAL  BOTANY 


453.  Competition  and  emigration.  A  little  has  already  been 
said  (Sect.  137)  about  the  severe  competition  among  plants, 
which  often  allows  only  one  seed  among  many  thousands  to 
grow  into  a  new  plant.  This  competition  frequently  tends  to 
cause  plants  to  nourish  better  in  new  territory.  Other  white 
pines  would  find  it  almost  impossible  to  grow  up  from  the 
seed  under  adult  trees  like  those  of  Fig.  321,  but  seeds  blown 


FIG.  373.  A  wooded  river  bank  invaded  by  a  moving  sand  dune 
In  the  foreground  a  young  cottonwood  is  being  covered  by  sand 

into  neighboring  clearings  (Fig.  322)  or  among  young  birches 
or  other  deciduous  trees  (Fig.  323)  may  promptly  begin  their 
growth  into  forest  trees.  In  this  way  there  is  a  constant  inva- 
sion of  neighboring  species  into  any  territory  not  already  occu- 
pied by  those  species  or  by  others  which  they  cannot  crowd 
out  of  the  way.  A  newly  formed  island  in  a  river  (Fig.  372), 
the  recently  drained  bed  of  a  lake  or  a  bayou,  is  promptly 
populated  by  the  plants  which  crowd  in  from  adjacent  terri- 
tory. The  newcomers  may  arrive  as  seeds,  or  as  cuttings, 


REGIONAL  DISTRIBUTION  501 

pieces  of  rootstocks,  or  even  as  entire  plants  washed  down 
by  the  stream.  Such  immigration  among  plants  is  in  accord- 
ance with  the  principle  known  as  following  the  line  of  least 
resistance;  that  is,  immigration  occurs  whenever  and  wher- 
ever a  more  densely  populated  area  is  in  contact  with  one 
less  densely  populated,  or  when  a  set  of  plants  of  superior 
qualifications  to  occupy  a  given  territory  comes  into  contact 
with  a  set  less  well  qualified. 

454.  Plants  able  to  meet  the  conditions  of  their  environment ; 
exceptions.  A  little  observation  and  reading  is  enough  to  con- 
vince the  student  that  the  plants  of  a  region  usually  meet 
fairly  well  the  requirements  of  its  soil  and  climate.  That  is 
to  say,  wild  plants  occur  where  they  do,  largely  because  of 
the  fact  that  when  they  migrated  into  the  area  which  they 
now  occupy  they  were  well  equipped  to  contend  with  other 
plants  and  hold  their  own  in  this  environment;  or  because, 
after  immigrating,  they  developed  characteristics  which  en- 
abled them  to  succeed.  If  a  considerable  piece  of  land  with 
its  flora  could  be  transplanted  bodily  from  the  arctic  regions 
to  the  most  fertile  part  of  the  tropics,  its  vegetation  would  be 
promptly  destroyed  by  the  new  climatic  conditions  or  by  the 
luxuriant  growth  which  would  invade  it  from  every  side.  On 
the  other  hand,  if  a  piece  of  ground  covered  with  tropical 
vegetation  were  carried  into  arctic  winter  conditions,  its  plant 
life  would  perish  of  cold  in  a  few  hours. 

Exceptions  to  the  rule  that  plants  are  found  growing  in  the 
places  that  suit  them  fairly  well  are  not  uncommon.  A  little 
has  already  been  said  (Sect.  434)  about  the  extraordinary  way 
in  which  some  plants  multiply  on  first  being  brought  into  terri- 
tory new  to  them.  Some  of  the  most  noteworthy  instances 
of  displacement  of  native  plants  by  foreign  species  have  oc- 
curred in  New  Zealand.  There  many  large,  robust  plants, 
some  of  them  very  spiny  and  growing  in  masses  impenetrable 
by  cattle,  have  been  replaced  by  European  grasses  and  clovers. 
The  sweetbrier  destroys  pastures  and  also  drives  out  native 
shrubs;  and  the  black  locust,  with  its  rapid  growth  and 


502  PEACTICAL  BOTANY 

numerous  suckers  from  the  roots,  quickly  gets  a  footing  and 
holds  its  ground  to  the  exclusion  of  most  other  vegetation. 
In  1855  only  44  species  of  foreign  plants  had  become  natural- 
ized in  New  Zealand,  while  in  1895  the  number  had  increased 
to  500  or  more.  Evidently  the  newcomers  have  qualifications 
which  enable  them  to  succeed  better  than  many  native  plants.1 

Botanists  are  coming  to  recognize  more  clearly  than  ever 
before  that  multitudes  of  plants  grow  under  conditions  which 
are  really  unfavorable  for  them.  It  is  thought  that  they  do 
so,  occurring  in  abundance  in  uncongenial  stations  and  infre- 
quently amid  better  surroundings,  because  the  unfavorable 
conditions  are  so  severe  as  largely  to  exclude  the  competition 
of  other  plants.  For  example,  knotgrass,2  knawel,3  milk  purs- 
lane,4 and  cudweed5  do  not  grow  in  much-trodden  paths  be- 
cause they  are  benefited  by  being  trampled  and  by  having  to 
root  themselves  in  hard  soil,  but  because  in  such  paths  they 
are  not  crowded  and  so  overshadowed  by  taller  weeds.  Seed 
plants  which  usually  grow  on  nearly  bare  rocks,  as  on  cliff 
sides,  generally  flourish  better  (with  an  equally  favorable 
light  supply)  in  richer  and  moister  soil.  Desert  plants,  as 
many  cacti,  often  grow  more  luxuriantly  under  conditions  of 
soil  and  climate  such  as  suit  ordinary  mesophytes.  The  com- 
mon groundsel,6  which  abounds  on  the  clean  sand  of  some 
Mediterranean  beaches,  blossoming  and  seeding  with  an  un- 
branched  stem  only  about  an  inch  high,  in  fertile,  fairly  moist 
soil  may  grow  to  a  height  of  18  inches. 

It  is  not  safe  to  assume  of  any  species  that  the  territory  or 
station  in  which  it  most  commonly  grows  is  the  best  adapted  to 
its  needs.  Such  a  statement  could  only  be  made  with  assurance 

1  On  the  subject  of  the  spread  of  species  introduced  into  new  territory 
see  Darwin,  Origin  of  Species,  chap,  iii ;  Gray,  essay  on  "The  Pertinacity 
and  Predominance  of  Weeds,"  in  Scientific  Papers  of  Asa  Gray,  edited  by 
Sargent  (Houghton  Mifflin  Company,  Boston,  1889) ;  also  weed  reports  of 
the  state  agricultural  experiment  stations  and  of  the  United  States  Depart- 
ment of  Agriculture. 

2  Polygonum  aviculare.  8  Scleranthus  annuus.          4  Euphorbia  maculata. 

6  Gnaphalium  uliginosum.  6  Senecio  vulgaris. 


REGIONAL  DISTRIBUTION  503 

after  careful  endeavors  to  introduce  the  plant  into  all  the 
kinds  of  environment  in  which  it  might  have  a  fair  chance  of 
success.  The  student  will  find  it  most  instructive  to  watch 
for  instances  of  the  occurrence  of  roadside  weeds,  such  as 
knotgrass,  wild  peppergrass,  Indian  chickweed,  and  dog  fennel, 
in  deep,  rich  ground,  or  to  plant  these  and  similar  tramp  plants 
in  good  soil  and  observe  how  they  succeed. 

455.  Plant  geography  of  the  United  States.  Briefly  stated, 
the  four  great  vegetation  areas  of  the  continuous  territory  of 
the  United  States 1  may  be  designated  as  follows : 

(1)  The  eastern  and  central  forest  region,  occupying  the  east- 
ern and  central  portions  of  the  country.  It  extends  westward 
to  an  irregular  boundary  line,  lying  mostly  to  the  east  of  the 
hundredth  meridian.  The  easternmost  portions  of  this  bound- 
ary run  considerably  east  of  the  Mississippi  River,  while  the 
westernmost  extend  at  least  500  miles  west  of  the  river. 

(2)  The  Plains  region,  stretching  westward  from  the  forest 
region  to  the  Rocky  Mountain  plateau. 

(3)  The  Rocky  Mountain  region,  including  the  Rocky  Moun- 
tains, the  Sierra  Nevada,  and  the  plateaus  between  them. 

(4)  The  Pacific  slope,  extending  from  the  Cascade  Range 
and  the  Sierra  Nevada  to  the  Pacific  coast. 

It  must  be  understood  that  the  same  species  of  plant  may 
occur  in  several  or  even  in  all  of  these  regions. 

Compare  the  temperature  requirements  of  the  white  pine 
and  bald  cypress  (as  far  as  shown  by  the  maps  on  page  504). 

Do  the  ranges  of  the  two  anywhere  overlap  ?   If  so,  where  ? 

Consult  Fig.  380  and  compare  the  moisture  requirements 
of  the  two  trees  (as  far  as  shown  by  the  maps). 

Which  species  avoids  the  Appalachian  highlands?  What 
two  reasons  may  be  given  for  this  ? 

In  using  the  maps  shown  in  Figs.  374  and  375  it  should 
be  kept  in  mind  that  they  are  not  drawn  to  exactly  the 
same  scale. 

1  That  is,  excluding  Alaska,  Porto  Rico,  the  Hawaiian  Islands,  and  the 
Philippines. 


FIG.  374.  Map  of  distribution  of  white  pine 

Modified  after  R.  B.  Hough.    "  Handbook  of  the  Trees  of  the  Northern  States 

and  Canada  " 


FIG.  375.  Map  of  distribution  of  bald  cypress 

Modified  after  R.  B.  Hough 

604 


REGIONAL  DISTRIBUTION  505 

456.  The  eastern  and  central  forest  region.  This  region  con- 
tains more  species  of  useful  hard  woods  than  any  similar  area 
within  the  temperate  zones.    The  oaks  are  the  leading  timber 
trees,  but  others,  as  the  hickory,  the  tulip  tree,  and  the  sassa- 
fras, are  of  especial  interest  to  botanists  as  characteristic  Amer- 
ican species.  The  northeasterly  part  of  the  forest  region,  while 
it  contains  many  hard-wood  genera,  such  as  beeches,  elms,  and 
maples,  is  notable  for  its  conifers.    Chief  among  these  are  the 
pines  (Fig.  321),  spruces,  hemlocks,  and  white  cedars  (Thuja). 
In  the  southerly  part  are  several  species  of  conifers,  such  as 
bald  cypress  (Fig.  19)  and  long-leaf  pine  (Fig.  260),  together 
with  such  hard  woods  as  walnuts,  hickories,  beeches,  chest- 
nuts, oaks,  elms,  magnolias,  sycamores,  and  ashes.    These  are 
deciduous  mesophytes,  but  there  are  some  water-loving  trees, 
such  as  the  water  hickory,  the  sweet  bay,  and  the  anise  tree, 
in  the  moister  parts  of  the  South,  which  may  fairly  be  ranked 
as  hydrophytes.    Some  trees,  as  the  bald  cypress,  may  grow 
either  as  hydrophytes  or  mesophytes. 

The  forest  region  has  always  contained  extensive  treeless 
areas.  The  earliest  settlers  found  "  openings "  in  the  hard- 
wood forests,  and  extensive  prairies,  marshes,  and  heaths,  all 
nearly  or  quite  destitute  of  trees.  Of  course  the  tendency 
under  cultivation  has  been  greatly  to  decrease  the  tree-cov- 
ered area,  and  it  is  now  very  unusual  to  find  bits  of  primeval 
forest  like  those  shown  in  Figs.  319  and  320. 

Since  the  forest  region  extends  more  than  1500  miles  north 
and  south,  it  contains  plants  ranging  all  the  way  from  sub- 
arctic species,  such  as  the  dwarf  herbaceous  willow,  saxifrages, 
and  crowberry,  to  sub-tropical  ones,  such  as  palms  and  ma- 
hoganies. 

457.  The  Plains  region.    The  prairies  of  the  Middle  West 
merge  imperceptibly  into  the  Great  Plains,  which  terminate,  at 
an  elevation  of  5000  feet  or  more,  in  the  beginnings  of  the 
Rocky  Mountain  system.    The  prairies  of  western  Kansas, 
western  Iowa,  Minnesota,  Nebraska,  and  South  Dakota  have 
less  than  20  per  cent  of  wooded  surface,  and  the  high  plains 


506 


PRACTICAL  BOTANY 


are  bare  of  trees  except  where  they  have  been  planted  or  occur 
naturally  in  belts  along  the  streams.  Some  of  the  principal 
reasons  that  have  been  given  for  the  treeless  condition  of  the 
prairies  and  the  plains  are  the  frequency  with  which  prairie 
fires  were  set  by  the  Indians,  the  scanty  rainfall,  and  the  de- 
structive effect  of  violent  dry  winter  winds,  acting  on  the  trees 

when  they  can  get  no  water 
from  the  frozen  soil.  Ex- 
cessive evaporation,  due  to 
exposure  to  high  winds  at 
all  seasons,  seems  to  be  a 
cause  of  prairies.  Such 
winds  are  particularly  fa- 
tal to  seedling  trees  which 
are  not  yet  deeply  rooted. 
Large  areas  also  have  never 
been  reforested  since  their 
vegetation  was  swept  away 
by  great  geological  changes 
in  the  Mississippi  Basin.1 

The  prairies  in  their  nat- 
ural condition  were  rather 
closely  covered  by  coarse 
grasses,  forming  a  very 
tough  sod.  This,  when 
turned  over  by  the  break- 
ing plow,  was  firm  and  durable  enough  to  be  used  by  the 
early  settlers  for  the  walls  of  sod  houses.  Among  the  prairie 
grasses  are  found  several  plants  of  the  Pea  family,  such  as  the 
lead  plant  or  shoe  strings,2  prairie  clover,3  ground  plum,4  and 
some  others.  Composites  are  very  abundant  and  characteristic, 
among  them  being  goldenrods  and  asters,  the  blazing  star,5  the 
cone  flower,6  and  several  species  of  tickseed.7  Some  sunflowers 8 

1  See  Pound  and  Clements,  Phytogeography  of  Nebraska,  Vol.  I,  pp.  67-70. 

2  Amorpha  canescens.        8  Petalostemum.        4  Astragalus.        6  Liatris. 

•  Budbeckia.        7  Coreopsis.        8  Helianthus. 


FIG.  376.  Occurrence  of  trees  above  the 

ordinary  timber  line,  in  sheltered  valleys 

and  ravines,  Rocky  Mountains 


REGIONAL  DISTRIBUTION 


507 


and  rosinweeds1  are  among  our  largest  herbaceous  prairie 
plants,  reaching  a  height  of  ten  or  more  feet  and  forming  a 
striking  feature  in  most  prairie  landscapes  in  late  summer 
and  autumn. 

In  their  eastern  portion  the  treeless  areas  of  the  high  plains 
are  largely  covered  by  close  mats  of  short  xerophytic  grasses 
known  as  buffalo  grass2  and 
grama  grass.3  Some  prickly- 
pear  cacti,4  milkweeds,5  and 
thistles6  are  also  found.  In 
early  July  the  grasses  dry 
up,  and  then  hardly  any 
vegetation  remains  alive 
aboveground  except  the 
succulent  cacti. 

The  western  portion  of 
the  high  treeless  plains  is 
the  beginning  of  the  foot- 
hill region,  of  high,  rather 
barren  table-lands,  extend- 
ing from  Montana  to  New 
Mexico  inclusive,  with  an 
altitude  in  many  portions 

of  5000  feet  above  sea  level.     FlG'  377«   °ne-sided  g™wth  of  trees 

near  timber  line  due  to  severe  winds 

Among  the  most  character-  f  rom  one  direction.  Rocky  Mountains 
istic  woody  plants  of  the 

region  are  several  wormwoods,  especially  the  sagebrush,7  and 
(in  "  alkali "  soils)  the  greasewood.8  The  sagebrush  (Fig. 
378)  is  highly  xerophytic,  with  deep  roots,  small  leaf  area, 
and  hairy  surface. 

458.  The  Rocky  Mountain  region.  The  Rocky  Mountain 
region  includes  the  most  diverse  formations,  ranging  from 
coniferous  forest  to  alpine  meadow  Characteristic  conifers  are 
several  true  spruces,  the  Douglas  spruce,9  and  a  considerable 

1  Silphium.  2  Bulbilis,  8  Bouteloua,  4  Opuntia,  5  Asclepias* 
6  Cirsium.  7  Artemisia  tridentatGr  3  fiarvobatus  vermiculatus  9  Pseudotsuga* 


508 


PKACTICAL  BOTANY 


FIG.  378.   A  twig 
of  sagebrush 

Modified  after 
Schimper 


number  of  pines.  The  alpine  flora,  occurring 
on  the  mountains  toward  the  timber  line  and 
above  it,  comprises  many  beautiful  herbaceous 
and  shrubby  species.  The  "alkali"  regions, 
with  a  highly  saline  soil,  abound  in  such  hal- 
ophytes  as  the  salty  sage,1  the  greasewood,2 
the  glasswort,3  and  the  Western  blite.4  The 
best  known  of  these  saline  areas  is  the  Great 
Basin,  covering  an  extensive  area  to  the  east 
of  the  Sierra  Nevada,  extending  nearly  to 
the  Great  Salt  Lake.  It  is  desolate,  treeless, 
and  without  grass.  The  less  saline  valleys 
and  the  foothills  are  covered  with  sagebrush, 
while  the  lower  and  more  "alkaline"  valleys 
are  tenanted  by  such  decided  halophytes  as 
those  just  named. 

In  the  southern  part  of  the  region  of  the 
Rocky  Mountain  system  and  to  the  south- 
west are  found  some  of  the  principal  deserts 
of  the  United  States,  such  as  the  Mohave  Des- 
ert, the  Ralston  Desert,  and  in  southern  Cali- 
fornia the  Colorado  Desert.  In  some  of  these 
the  temperature  for  long  periods  in  the  sum- 
mer ranges  as  high  as  118°  F.,  and  the  total 
annual  rainfall  may  be  less  than  an  inch.  Ex- 
treme xerophytes,  such  as  cacti,  a  few  palms, 
and  tree  yuccas  (Fig.  379),  abound. 

459.  The  Pacific  slope.  The  summer  and 
the  winter  climate  of  the  Pacific  coast  region 
differ  in  temperature  much  less  than  do  por- 
tions of  the  Atlantic  coast  in  the  same  lati- 
tude. In  the  southern  part  of  the  region  the 
most  striking  difference  between  seasons  is 
the  contrast  between  their  amount  of  rainfall. 


1  Atriplex. 

2  Sarcobatus  vermiculatus* 


3  Salicornia. 
*  Suceda. 


REGIONAL  DISTRIBUTION 


509 


FIG.  379.   Tree  yucca  in  the  Mohave  Desert 
Redrawn  from  a  photograph  by  Coville 

At  Stanford  University,  thirty  miles  south  of  San  Francisco, 
the  rainy  season  usually  begins  in  October  and  lasts  until 
April.  June,  July,  August,  and  September  are  usually  rain- 
less. At  San  Diego  the  dry  season  begins  in  April  and  lasts 
for  seven  months.  Vegetation  begins  with  the  autumn  rains 


510 


REGIONAL  DISTRIBUTION  511 

and  is  merely  accelerated  by  the  coming  of  warm  weather  in 
the  spring.  Most  herbaceous  plants  cease  to  grow  soon  after 
the  summer  drought  has  set  in,  so  that  the  face  of  the  country 
is  parched  and  in  places  seems  almost  lifeless. 

The  northern  portion  of  the  Pacific  slope,  through  the 
states  of  Washington  and  Oregon,  is  divided  by  the  Cascade 
Mountains  into  a  comparatively  moist  western  region  and  a 


FIG.  381.  Annual  rainfall  of  the  United  States 

Darkest  shade,  over  80  inches ;  lighter  vertical  lines,  from  40  inches  to  80  inches ; 

horizontal  lines,  from  20  inches  to  40  inches ;  blank,  from  10  inches  to  20  inches ; 

dotted,  less  than  10  inches.  After  W.  M.  Davis,  "  Physical  Geography  " 

much  drier  (sometimes  semi-desert)  eastern  region.  This  is 
due  to  the  fact  that  the  Cascade  Range,  running  in  a  general 
north-and-south  direction,  causes  the  precipitation,  in  the  form 
of  rain  or  snow,  of  most  of  the  moisture  brought  from  the 
Pacific  by  the  southwest  winds.  These  mountains  are  heav- 
ily timbered,  especially  along  their  western  slope,  and  the 
dense  forests  abound  in  such  valuable  coniferous  trees  as  the 
western  white  pine,1  several  species  of  true  fir,2  and  the  west- 
ern hemlock.3  West  of  the  Cascades  three  of  the  principal 

1  Pinus  monticola.  2  Abies.  8  Tsuga  heterophylla. 


512  PRACTICAL  BOTANY 

conifers  are  the  giant  cedar,1  red  fir,2  and  Sitka  spruce.3  In 
the  bottom  lands  of  Washington,  especially  along  rivers,  there 
are  found,  besides  some  conifers,  groves  of  poplar,  maple,  and 
ash.  In  the  wettest  of  these  lands  occur  dense  thickets  of 
willows,  Western  cornel,  crab  apple,  and  vine  maple. 

Much  of  eastern  Washington  has  an  annual  rainfall  of 
not  more  than  ten  inches,  and  is  generally  covered  with  sage- 
brush and  with  other  semi-desert  vegetation,  although  the  soil 
when  irrigated  is  extremely  fertile.  Southeastern  Oregon  is 
in  great  part  a  rocky,  sterile  plateau  of  volcanic  origin,  with 
vegetation  consisting  largely  of  sagebrush,  dwarf  pine,  and 
juniper. 

From  the  forty-first  to  the  thirty-fifth  parallel  (beginning 
a  little  to  the  south  of  the  Oregon  line)  the  southern  portion 
of  the  Pacific  slope  is  characterized  by  the  California  ever- 
green conifers,  the  sugar  pine  4  of  the  coast  region,  the  yellow 
pine,5  and  others.  Two  redwoods  are  notable  among  the  moun- 
tain flora,  —  the  smaller6  a  very  important  source  of  lumber, 
the  larger7  (big  tree  or  giant  redwood)  the  greatest  and  most 
imposing  of  all  trees  (Figs.  250  and  260). 

Among  the  characteristic  members  of  the  California  flora 
are  many  xerophytic  shrubs  and  small  trees,  in  appearance 
not  unlike  the  abundant  thickets  of  some  parts  of  the  Medi- 
terranean coast  region.  The  California  thickets,  known  as 
chaparral,  contain  many  leathery-leaved  evergreen  dicotyle- 
dons, among  them  members  of  the  Oak,  the  Rose,  the  Sumach, 
the  Heath,  the  Buckthorn,  and  the  Composite  families. 

On  account  of  the  long  and  severe  dry  season,  southern 
California  abounds  in  deep-rooted  and  in  bulb-bearing  plants, 
many  of  the  latter  belonging  to  the  Lily  family ;  and  in  and 
about  the  deserts  are  many  cacti  and  other  succulent  plants, 
together  with  numerous  xerophytic  shrubs  which  are  not 
succulent. 

1  Thuja  plicata.  2  Pseudotsuga  mucronata.  8  Picea  sitchensis.  4  Pinus 
Lambertiana.  6  P.  ponderosa.  6  Sequoia  sempervirens.  7  S.  Washinytoniana, 


REGIONAL  DISTRIBUTION  513 

460.  Influence  of  rainfall  on  forest  distribution.  Plant  forma- 
tions in  general,  and  forest  ones  among  the  rest,  have  their 
boundaries  determined  largely  by  the  amount  and  seasonal 
distribution  of  the  annual  rainfall  of  the  region.  A  careful 
comparison  of  the  forest  map  of  the  United  States  (Fig.  380) 
with  the  rainfall  map  (Fig.  381)  shows  that  the  arid  and  semi- 
arid  regions  are  treeless.  By  far  the  greater  portion  of  the 
immense  area  lying  to  the  west  of  an  irregular  line  extending 
from  the  Red  River  of  the  North  to  the  junction  of  the  Pecos 
with  the  Rio  Grande,  has  an  annual  rainfall  ranging  from 
twenty  inches  down  to  almost  nothing.  Over  this  great  ter- 
ritory there  are  few  extensive  forests  except  those  covered 
with  xerophytic  conifers,  and  these  occur  mostly  in  the  moun- 
tains where  the  rainfall  is  somewhat  greater.  Our  true  deserts 
are  treeless  except  for  scattered  individuals  of  such  extreme 
xerophytes  as  the  tree  yucca  (Fig.  379).  The  Pacific  slope, 
in  its  northern  portion,  has  an  annual  rainfall  of  thirty-seven 
inches,  and  is  covered  with  such  luxuriant  forests  as  are  shown 
in  Fig.  262.  The  southern  portion  has  an  average  annual  rain- 
fall of  ten  inches,  and  (except  on  the  mountains)  has  no  con- 
siderable forests  but  only  a  scanty  growth  of  trees  and 
xerophytic  shrubs  (chaparral). 


APPENDIX 


INFLORESCENCE 

The  manner  in  which  flowers  are  arranged  on  the  floral  axis  or 
flower-bearing  portion  of  the  stem  is  called  inflorescence.  Some- 
times the  flower  clusters  themselves  are  also  called  inflorescences. 

Each  flower,  like  a  vegetative  branch,  usually  arises  from  the  axil 
of  a  leaf  (Fig.  1,  -4),  but  leaves  along  the  floral  axis  are  often  minute, 
sometimes  even  scale-like  in  appearance  (Fig.l,.B;  Fig.  4,  £).  All 
such  reduced  leaves  are  known  as  bracts,  and  when  they  arise  from 
branches  of  the  main  axis,  as  in  Fig.  6,  A,  they  are  called  bractlets. 

There  are  two  main  types  of  inflorescence  which  are  distin- 
guished by  the  relative  development  of  the  main  axis  and  of  the 
lateral  axes.  In  the  racemose  type  of  inflorescence  the  main  axis 
is  more  strongly  developed  than  the  lateral  ones  and  overtops 
them,  while  in  the  cymose  type  the  lateral  axes  extend  beyond 
the  main  one.  Some  of  the  principal  kinds  of  flower  clusters  are 
shown  in  the  figures  which  follow. 

CLUSTERS  OF  THE  RACEMOSE  TYPE  (INDETERMINATE 
INFLORESCENCE) 


FIG.  1.  A,  axillary  and  solitary  flowers  of  pimpernel  ; 

red  currant 

p,  peduncle;  p',  pedicel;  6r,  bract 
515 


,  raceme  of  common 


516 


PRACTICAL  BOTANY 


A  B 

I  II 

FIG.  2.    I,  simple  umbel  of  cherry  ;  II,  catkins  of  willow 
A,  staminate  flowers ;  B,  pistillate  flowers 


FIG.  3.  A,  spike  of  plantain  ;  B,  head  of  red  clover 


APPENDIX 


517 


ch 


B 


FIG.  4.  Head  of  yarrow 

A,  top  view  (magnified);  B,  lengthwise  section  (magnified),    re,  receptacle;  i, 

involucre;  r,  ray  flowers;  d,  disk  flowers;  c,  corolla;  s,  stigma;  ch,  chaff  or 

bracts  of  receptacle 


A  B 

FIG.  5.  A,  panicle  of  oat ;  B,  compound  umbel  of  carrot 


518 


PEACTICAL  BOTANY 


\ 


p 


A  BCD 

FIG.  6.  Diagrams  of  inflorescence 
panicle ;  B,  raceme ;  C,  spike ;  Z),  head ;  E,  umbel 


CLUSTERS  OF  THE  CYMOSE  TYPE  (DETERMINATE  INFLORESCENCE) 


FIG.  7    Compound  cyme  of  mouse-ear  chickweed 
t,  the  terminal  (oldest)  flower 


APPENDIX  519 

SUMMARY  OF  PRINCIPAL  KINDS  OF  FLOWER  CLUSTERS 

A.  Indeterminate  inflorescence.    Order  of  blossoming  from  below  up- 
ward, or  from  without  inward 

1.  Axillary  flowers.    Flowers  growing  in  the  axils  of  ordinary 

leaves. 

2.  Raceme.    Flowers  with  flower  stalks,  called  pedicels,  arranged 

along  the  peduncle  or  stem  in  the  axils  of  special  (usually 
pretty  small)  leaves  called  tracts. 

3.  Corymb.    Flowers  arranged  as  in  the  raceme,  but  with  the 

lower  pedicels  so  lengthened  as  to  make  the  flower  cluster 
flat  or  nearly  so  (as  in  the  hawthorn  or  the  yarrow). 

4.  Umbel.    Flowers  with  pedicels  of  nearly  equal  length,  all  appear- 

ing to  spring  from  a  common  point,  like  the  ribs  of  an  um- 
brella. An  involucre  of  bracts  usually  surrounds  the  bases 
of  the  pedicels. 

5.  Spike.   Flowers  as  in  the  raceme,  but  sessile  ;  that  is,  without 

pedicels. 

6.  Head.   Flowers  as  in  the  spike,  but  the  cluster  nearly  globular. 

7.  Panicle.   Flowers  as  in  the  raceme,  but  the  cluster  made  com- 

pound by  the  branching  of  the  peduncle. 

B.  Determinate    inflorescence.     Order    of    blossoming    from    within 
outward. 

1.  Flower  terminal.   One  flower  borne  at  the  summit  of  the  stem. 

2.  Cyme.    Flowers  much  as  in  the  umbel,  but  the  innermost  blos- 

soming first. 


GLOSSARY 


Abortive.    Imperfectly  developed,  as  in  abortive  stamens. 

Absorption.    Act  of  taking  in  substances  through  the  tissues. 

Accessory  fruits.  Fruits  reenforced  by  ripening  of  stem  or  other  struc- 
tures together  with  ordinary  fruits,  as  in  strawberry,  apple,  pear,  quince. 

Adventitious  buds.  Buds  that  spring  from  various  parts  of  the  root 
or  stem,  not  from  nodes. 

Aerial  roots.    Roots  that  develop  in  the  air. 

Akene.  A  small,  dry,  one-seeded  fruit  in  which  the  ovary  wall  adheres 
to  the  seed,  as  in  sunflower,  dandelion,  and  grains  of  common  cereals. 

Albuminous  seeds.    Seeds  that,  when  ripe,  contain  endosperm. 

Aleurone.  Grains  of  definite  structure  containing  protein  food;  aleu- 
rone  grains  are  often  found  in  a  single  layer  of  regular  cells  just  within 
the  seed  coat. 

Alternation  of  generations.  Alternating  of  a  sexual  and  a  sexless  gen- 
eration in  the  life  cycle  of  a  plant. 

Ament.    The  flower  cluster  of  trees  and  shrubs,  such  as  oak,  willow,  etc. 

Anabolism.  Building-up  processes ;  making  and  assimilating  food 
materials. 

Anaerobes.  Plants  that  cannot  carry  on  their  life  processes  in  presence 
of  ordinary  air. 

Anatropous  (turned  up).  Applied  to  ovules  or  seeds  that  grow  in  an 
inverted  position. 

Androecium  (male  household).  Stamens  of  a  flower  collectively ;  this 
name  was  given  when  stamens  were  thought  to  be  male  sex  organs. 

Anemophilous  flowers  (wind-loving  flowers).  Those  whose  fertiliza- 
tion is  effected  by  means  of  the  wind. 

Angiosperms  (inclosed  seeds).  One  of  the  two  groups  of  spermato 
phytes  (seed  plants). 

Annulus  (a  ring).  The  elastic  ring  of  cells  around  the  sporangium 
in  ferns. 

Anther.    The  pollen-bearing  part  of  the  stamen. 

Antheridiophores.    Stalks  upon  which  antheridia  are  borne. 

Antheridium ;  pi.  antheridia.  The  male  sex  organ  in  the  lower  groups 
of  plants. 

Antherozoid.    See  Sperm. 

620 


GLOSSARY  521 

Antipodal  (against  the  foot).  Applied  to  a  group  of  cells  at  the  en4 
of  the  eirbryo  sac  farthest  from  the  micropyle. 

Apetalcns.   Without  petals. 

Apical.    At  the  apex  or  tip. 

Apocarpous  (without  carpels).  Applied  to  flowers  in  which  the  car- 
pels  are  entirely  free  from  one  another. 

Appressed.    Lying  flat  throughout  its  length,  as  appressed  bracts. 

Association.  An  ecological  unit  group  smaller  than  a  plant  forma- 
tion, of  which  the  latter  is  sometimes  made  up. 

Awl-shaped.    Narrow,  tapering  to  a  point,  as  awl-shaped  leaves. 

Awned.  Having  bristle-like  appendages,  as  in  heads  of  many  kinds 
of  wheat. 

Basidium  (club) ;  pi.  basidia.  The  specialized  club-shaped  cells  on 
which  the  spores  of  some  fungi  are  borne. 

Bast.  The  phloem  portion  of  a  fibrovascular  bundle.  It  may  be 
fibrous  (hard  bast),  or  composed  of  sieve  tubes  (soft  bast). 

Bilabiate  (two-lipped).  Applied  to  the  form  of  corolla  in  certain  di-' 
cotyledonous  plants. 

Bract  (a  thin  plate).  The  small,  scale-like,  modified  leaves  which 
sometimes  are  found  at  the  base  of  the  flower  cluster. 

Calyptra  (a  cover).  In  mosses,  the  hood  that  covers  the  tip  of 
the  capsule. 

Calyx  (a  cup).  All  the  sepals,  which  together  form  the  outer  enve- 
lope of  a  flower. 

Cambium.  The  meristem  cells  of  a  fibrovascular  bundle  lying  be- 
tween the  phloem  and  xyleni,  and  having  the  power  of  division,  so  as 
to  produce  new  phloem  and  xylem. 

Capitate  (relating  to  head).  (1)  Rounded,  as  the  head  of  the  stigma 
of  the  primrose ;  or  (2)  growing  in  heads. 

Capsule  (a  small  box).  A  dry,  dehiscent  seed  vessel  (formed  of  more 
than  one  carpel). 

Carpel  (fruit).  The  megasporophyll ;  hence  either  a  simple  pistil  or 
one  of  the  parts  of  a  compound  pistil. 

Carpellary.    Relating  to  a  carpel. 

Catkins.    See  Ament. 

Caulicle  (a  small  stem).    The  initial  stem  in  an  embryo. 

Cell.  The  morphological  or  anatomical  unit  of  plant  and  animal 
structure. 

Cellulose  (pertaining  to  a  cell).  The  primary  substance  of  the  cell  wall. 

Central  cylinder.  The  stele,  or  portion  of  the  root  or  stem  which  is 
inclosed  by  the  primary  cortex. 

Chaff.  Small  dry  scales  usually  found  in  connection  with  the  seeds 
of  plants,  as  in  grasses  and  Composites. 


522  PRACTICAL  BOTANY 

Chalaza.  The  base  of  an  ovule  where  integuments  and  nucellus  are 
one  common  tissue. 

Chlorophyll  (green  leaf).    The  green  coloring  matter  of  plants. 

Chloroplast.  One  of  the  special  bodies  that  contain  chlorophyll. 

Choripetalous  (separate  petals).  With  the  petals  separate,  not  united. 

Chromatophore  (color-bearing).  A  general  term  for  all  bodies  in 
plants  containing  coloring  matter. 

Cilium  (eyelash) ;  pi.  cilia.  Marginal  hairs ;  motile  protoplasmic  fila- 
ments, as  those  of  sperms. 

Cleistogamous.  With  close  fertilization,  occurring  in  flowers  before 
they  open. 

Closed  bundle.  A  fibrovascular  bundle  containing  no  cambium ;  growth 
is  closed. 

Coenocyte.  A  number  of  nucleated  masses  of  cytoplasm  (cells)  in- 
closed by  a  common  wall. 

Collateral  (sides  together).  Side  by  side,  as  in  a  fibrovascular  bundle 
in  which  the  xylem  and  phloem  are  side  by  side  in  a  radial  direction. 

Columella  (a  small  column).  The  persistent  axis  of  certain  spore 
cases,  as  in  mosses. 

Concentric  (center  together).  Technically  used  of  a  fibrovascular 
bundle  whose  tissues  are  arranged  so  as  to  surround  one  another. 

Conidiophore  (conidium-bearer).  Stalk  upon  which  conidia  are  borne. 

Conidium ;  pi.  conidia.  The  asexual  spore  of  some  fungi,  as  in  potato 
blight  and  grape  mildew. 

Conjugation  (joined  together).    The  sexual  union  of  similar  gametes. 

Connate.  Applied  to  leaves  that  appear  united  or  grown  together 
at  their  bases. 

Connective.  The  portion  of  the  stamen  connecting  the  parts  of 
the  anther. 

Cordate.    Heart-shaped. 

Corm.  The  fleshy  stem  or  base  of  a  stem ;  a  bulb-like  structure,  as 
on  the  underground  part  of  jack-in-the-pulpit. 

Corolla  (a  small  crown).  The  inner  envelope  of  a  flower  within  the 
calyx,  composed  of  petals. 

Cortex.    Rind  or  bark. 

Cortical.    Relating  to  cortex. 

Cotyledon.  A  primary  embryo  leaf  borne  by  the  hypocotyl  (caulicle) 
of  the  embryo  plant. 

Cryptogams  (hidden  marriage).  A  term  used  to  include  thallophytes, 
bryophytes,  and  pteridophytes. 

Cupule  (a  little  cup).    The  gemma  cup  of  liverworts. 

Cuticle  (skin).  The  outermost  layer  of  epidermis,  differing  chemically 
from  the  remainder  of  the  cell  wall. 


GLOSSARY  523 

Cutinization.  The  transformation  of  the  outer  layer  of  the  epidermis 
into  cutin,  a  substance  which  is  nearly  waterproof  and  not  easily  pene- 
trated by  gases. 

Cyclic.  An  arrangement  of  leaves  or  floral  organs  in  such  a  way 
that  two  or  more  appear  upon  the  axis  at  the  same  level,  thus  forming 
a  cycle  or  whorl. 

Cytoplasm.   The  jelly-like  living  material  of  the  cell. 

Deciduous.  Applied  to  plants  which  lose  their  leaves  at  regular 
intervals. 

Dehiscence  (gaping).  The  opening  of  an  organ  to  discharge  its  con- 
tents, as  in  case  of  anthers,  sporangia,  and  capsules. 

Dermatogen  (skin-producer).  The  layer  of  young  epidermis  in  grow- 
ing points. 

Dichogamous.  With  stamens  and  pistils  not  maturing  together,  as  in 
many  plantains. 

Dichotomous  (cutting  in  two).   Forked  regularly  in  pairs. 

Dicotyledonous  (cotyledons  double).  Having  two  cotyledons  or  seed 
leaves. 

Dimorphism  (two  structures).  Having  two  different  forms.  Long- 
styled  and  short-styled  flowers  of  the  same  species  are  dimorphous. 

Dioecious  (two  households).  Having  the  two  kinds  of  reproductive 
organs  borne  by  separate  individuals 

Dorsiventral.  Having  the  two  surfaces  differentiated  so  that  one  is 
upper  and  one  lower. 

Drupe.  A  stone  fruit  with  a  fleshy  outer  and  a  hard  inner  layer  of 
the  pericarp,  as  in  the  walnut,  peach,  plum,  etc. 

Ecology.  The  study  of  the  relations  between  the  plant  and  its  envi- 
ronment, including  the  other  living  beings  with  which  it  has  to  do. 

Egg  or  oosphere.    The  female  gamete. 

Egg  apparatus.  A  group  of  three  cells,  consisting  of  the  egg  and  two 
synergids,  one  at  each  side.  Found  in  angiosperms. 

Embryo.    The  young  plantlet  within  the  seed. 

Embryo  sac.    The  cavity  within  which  the  embryo  develops. 

Endodermis  (within  the  skin).  The  layer  of  cells  inclosing  the  fibro- 
vascular  bundle ;  the  bundle  sheath. 

Endogenous  (produced  within).    Originating  from  internal  tissues. 

Endosperm  (within  the  seed).  A  tissue  containing  reserve  materials 
developed  within  the  embryo  sac. 

Endosperm  nucleus.  The  nucleus  of  the  angiosperm  embryo  sac  from 
which  the  endosperm  of  the  embryo  sac  develops. 

Enzyme.  One  of  the  plant  secretions  which  digest  substances  ex- 
ternal to  the  plant,  as  in  carnivorous  plants,  or  reserve  materials,  as 
in  seeds. 


524  PRACTICAL  BOTANY 

Epiphyte.    A  plant  which  grows  upon  other  plants. 

Fertilization.    The  act  of  uniting  an  egg  and  a  sperm. 

Fibrovascular  bundles  (fiber  vessels).  The  strands  that  make  up  the 
framework  of  higher  plants. 

Filament  (a  thread).  The  stalk  of  the  stamen  that  supports  the 
anther ;  also  the  individual  threads  of  algae  or  fungi. 

Filiform.   Thread-like. 

Fission  (splitting).    Cell  division  resulting  in  division  into  halves. 

Fleshy.    Thick,  succulent. 

Flowering  glume.  In  grasses,  the  bract  that  subtends  each  flower, 
sometimes  called  lower  palet. 

Formation.  An  ecological  group.  It  signifies  a  well-defined  assem- 
blage of  plants  characteristic  of  some  kind  of  station. 

Frond  (a  leaf).    A  name  given  to  the  leaf  of  ferns. 

Fruit.    The  ripened  ovary  and  its  contents. 

Funiculus  (a  slender  rope).    The  stalk  of  an  ovule  or  seed. 

Gametangium  (gamete  vessel).  The  specialized  organ  for  production 
of  gametes. 

Gamete.  A  reproductive  cell  which  ordinarily  becomes  functional 
only  upon  union  with  another.  As  a  result  of  this  union  a  sexual  spore 
is  formed. 

Gametophyte  (gamete  plant).  The  sexual  stage  of  an  alternating  plant. 

Gemma  (a  bud) ;  pi.  gemmae.  In  bryophytes,  many-celled  buds  special- 
ized for  vegetative  propagation. 

Generative  cell.  The  cell  within  the  male  gametophyte  of  spermato- 
phytes  (usually  within  the  microspore  wall)  which  divides  to  form  the 
two  male  cells. 

Geotropism  (turning  toward  the  earth).  The  tendency  of  organs  or 
portions  of  organs  to  go  downward. 

Glaucous  (pale  green,  gray).  Whitened  with  a  bloom,  like  that  on 
a  cabbage  leaf. 

Glume  (a  husk).  A  chaff-like  bract  belonging  to  the  inflorescence  of 
grasses;  the  outer  glumes  subtend  the  spikelet;  the  flowering  glume 
is  the  bract  of  the  flower.  . 

Gluten  (glue).  A  term  used  for  the  glue-like  products  of  plants, 
especially  of  seeds. 

Grain.  A  seed-like  fruit,  like  those  of  grasses,  with  pericarp  grown 
fast  to  the  seed ;  also  any  small,  rounded  body,  as  of  starch. 

Growing  point.  The  group  of  meristem  cells  at  the  growing  tip  of 
an  organ,  from  which  the  various  tissues  arise. 

Guard  cells.    The  cells  (usually  two)  which  Open  and  close  a  stoma. 

Gymnosperms  (naked  seeds).  One  of  the  two  groups  of  spermato- 
phytes  (seed  plants). 


GLOSSARY  525 

Gynaecium  (female  household).  The  pistil,  or  collectively  the  pistils, 
of  a  flower. 

Halophyte.  A  plant  which  can  thrive  in  saline  soil,  as  that  of  "alkali" 
lands  or  salt  marshes. 

Haustorium  (drinking  organs) ;  pi.  haustoria.  The  absorbing  organs 
of  some  parasites. 

Heliotropism  (turning  to  light).  Tendency  of  plants  to  turn  toward 
the  sun. 

Heterogamy  (unlike  gametes).  The  condition  of  plants  whose  pairing 
gametes  are  dissimilar. 

Heterogamous.    Pertaining  to  heterogamy. 

Heterospory  (unlike  spores).  The  condition  in  plants  which  produce 
two  kinds  of  asexual  spores. 

Heterosporous.    Pertaining  to  heterospory. 

Homospory  (similar  spores).  The  condition  in  plants  which  produce 
but  one  kind  of  asexual  spore. 

Homosporous.    Pertaining  to  homospory. 

Host.  The  plant  upon  or  within  which  parasitic  plants  or  animals 
develop,  and  from  which  they  obtain  nourishment. 

Hybrid.  A  plant  which  is  the  offspring  of  an  egg  of  one  species  fer- 
tilized by  the  pollen  of  another  species.  The  term  is  also  used  for  crosses 
between  two  varieties  of  plants. 

Hydrophyte  (water  plant).  A  plant  thriving  only  in  water  or  marshes. 

Hygroscopic  (moisture  seeking).    Having  an  avidity  for  water. 

Hymenium  (a  membrane).  In  fungi,  a  surface  layer  of  interwoven 
filaments  from  which  the  spore-bearing  filaments  arise. 

Hypha  (a  web) ;  pi.  hyphse.  The  slender  vegetative  filaments  of  fungi 
which  may  or  may  not  be  woven  into  a  mat  (mycelium)  or  a  definitely 
organized  plant. 

Hypocotyl.    The  short  stem  of  an  embryo  seed  plant. 

Hypodermis  (under  the  skin).  The  tissues  » which  lie  immediately 
beneath  the  epidermis  and  which  serve  to  strengthen  it. 

Hypogynous  (being  under  the  ovary).  Applied  to  those  flowers  whose 
stamens  and  floral  envelopes  are  at  the  base  of  the  ovary. 

Indehiscent.    Not  dehiscent,  or  not  splitting  regularly. 

Indusium  (covering)  ;  pi.  indusia.  In  ferns,  a  cellular  outgrowth  of 
the  leaf  covering  the  clusters  of  sporangia  (son). 

Inflorescence  (flowering).  The  arrangement  of  flowers ;  or  the  flower- 
ing portion  of  a  plant. 

Integument  (covering).    The  covering  of  the  ovule. 

Intercellular.    Between  or  among  the  cells. 

Internode.    The  part  of  a  stem  between  two  nodes  or  joints. 

Intine  (on  the  inside).    The  inner  coat  of  a  pollen  grain. 


526  PRACTICAL  BOTANY 

Involucre  (rolled  within).  The  leaf-like  or  bract-like  sheath  that  in- 
closes a  cluster  of  flowers. 

Irritability.  The  capacity  which  protoplasm  possesses  of  respond- 
ing to  stimuli,  such  as  light,  heat,  gravity,  and  contact  with  chemical 
reagents. 

Isogamous  (equal  gametes).  Applied  to  those  plants  whose  pairing- 
gametes  are  similar. 

Lamina  (a  layer).    The  blade  or  expanded  part  of  a  leaf. 

Leaf  trace.  The  fibrovascular  bundles  from  the  leaf  which  blend  with- 
in the  stem  with  its  fibrovascular  cylinder. 

Xenticel.  A  round,  oval,  or  lens-shaped  opening  on  the  exterior  surface 
of  the  bark. 

Leucoplast  (white  molded).  A  minute  colorless  body  within  a  cell. 
When  exposed  to  light,  leucoplasts  may  develop  into  chloroplasts. 

Liana.    A  climbing  plant. 

Ligule  (a  small  tongue).  In  grasses  a  thin  appendage  at  the  junction 
of  leaf  blade  and  sheath. 

Medullary.  Relating  to  the  pith ;  medullary  rays  are  the  pith  rays 
which  radiate  to  the  bark  between  the  fibrovascular  bundles. 

Megasporangium  (large  spore  vessel).  The  sporangium  that  produces 
the  megaspores. 

Megaspore  (great  or  large  spore).  The  larger  one  of  the  two  kinds  of 
asexual  spores  produced  by  certain  pteridophytes  and  all  spermatophytes. 

Megasporophyll  (large  spore  leaf).  The  leaf  upon  which  the  mega- 
sporangium  develops. 

Meristem  (dividing  tissue).  Tissues  with  the  cells  all  nearly  alike 
and  still  capable  of  subdividing. 

Mesophyll  (middle  leaf).  The  green  or  soft  tissue  of  the  inner  part 
of  the  leaf. 

Mesophytes  (middle  plants).  Normal  land  plants  such  as  grow  in  an 
average  soil  and  under  a  moderate  climate. 

Metabolism.  Chemical  transformations  of  matter  carried  on  by  plants 
in  the  production  and  utilization  of  their  food  supply,  and  disposition 
of  waste  products. 

Micropyle  (small  gate).  The  opening  left  by  the  integuments  of  the 
ovule,  and  which  leads  to  the  nucellus. 

Microsporangium  (small  spore  vessel).  The  sporangium  that  produces 
the  microspore. 

Microspore  (small  spore).  The  smaller  spore  of  the  two  kinds  pro- 
duced by  certain  pteridophytes  and  all  spermatophytes. 

Microsporophyll  (small  spore  leaf).  The  leaf  upon  which  the  micro- 
sporangium  is  borne. 

Midrib.    The  central  or  main  rib  of  a  leaf  or  thallus. 


GLOSSARY  527 

Monoecious  (one  household).  Applied  to  those  plants  upon  one  of 
which  both  kinds  of  gametes  are  borne.  Strictly  speaking,  the  term 
applies  only  to  the  gametophyte  stage  of  plants.  A  monoecious  seed 
plant  bears  both  staminate  and  pistillate  flowers. 

Monopodial  (having  one  foot).  Said  of  a  stem  consisting  of  a  single 
and  continuous  axis  (footstalk). 

Mother  cell.  A  cell  that  produces  new  cells  (usually)  by  internal 
division. 

Mutualism.  A  symbiotic  relationship  in  which  the  organisms  are 
mutually  helpful. 

Mycelium  (fungous  growth).  The  filamentous  vegetative  growth  of 
fungi,  composed  of  hyphre. 

Naked.    Wanting  some  usual  covering. 

Nascent.    Developing  or  growing. 

Nastic  movements.  Movements  produced  by  all-round  stimuli,  as 
heat.  The  opening  and  closing  of  the  flowers  of  crocuses  and  tulips 
are  thermonastic  movements. 

Nectary.    The  structure  in  which  nectar  is  secreted. 

Nerve.    A  simple  vein  or  rib. 

Node  (a  joint).   That  part  of  a  stem  which  normally  bears  leaves. 

Nucellus  (a  little  kernel).  The  mass  of  the  ovule  within  the  in- 
teguments. 

Nucleolus  (diminutive  of  nucleus).  The  sharply  defined  rounded  part 
often  seen  in  the  nucleus. 

Nucleus  (a  kernel).  The  usually  roundish  mass  found  in  the  proto- 
plasm of  most  active  cells,  and  differing  from  the  rest  of  the  protoplasm 
in  its  greater  density. 

Oogonium;  pi.  oogonia.  The  female  reproductive  organ  of  thallophytes. 

Oosphere  (egg  sphere).  The  egg  cell;  the  mass  of  protoplasm  pre- 
pared for  fertilization. 

06'spore  (egg  spore).    The  egg  cell  after  fertilization. 

Open  bundle.    A  fibrovascular  bundle  which  contains  cambium. 

Operculum  (a  cover  or  lid) ;  pi.  opercula.  In  mosses  the  terminal  lid 
of  the  capsule,  just  beneath  the  calyptra. 

Osmosis.    The  interchange  of  liquids  through  a  membrane. 

Ovary  (egg-keeper).  That  part  of  the  carpel  in  which  the  ovules 
are  formed. 

Ovule  (an  egg).  The  body  which  becomes  a  seed  after  fertilization 
and  maturation ;  formerly  thought  to  be  an  egg. 

Palet  (chaff).    In  grasses,  the  inner  bract  of  the  flower. 

Palisade  cells.  The  elongated  parenchyma  cells  of  a  leaf,  which 
stand  at  right  angles  to  its  surface  and  are  often  confined  to  the  upper 
part  of  the  leaf. 


528  PRACTICAL  BOTANY 

Palmate  (pertaining  to  the  hand).  Radiating  like  the  fingers;  said 
of  the  veins  or  divisions  of  some  leaves. 

Panicle  (a  tuft).  A  loose  and  irregularly  branching  flower  cluster,  as 
in  many  grasses. 

Pappus  (down).    The  modified  calyx  of  the  composites. 

Paraphysis  (accompanying  organs)  ;  pi.  paraphyses.  Sterile  bodies, 
usually  hairs,  which  are  found  mingled  with  the  reproductive  organs  of 
various  lower  plants. 

Parasite.  An  organism  that  obtains  its  food  from  the  living  tissues 
or  the  secretions  of  other  organisms. 

Parenchyma.  Ordinary  or  typical  cellular  tissue,  i.e.  of  thin-walled 
cells  nearly  equal  in  all  their  dimensions. 

Parthenogenesis.  The  formation,  without  fertilization,  of  a  spore  which 
is  functionally  the  same  as  a  sexual  spore.  In  general  it  means  that  the  fe- 
male gamete  becomes  a  spore  directly,  and  may  grow  without  fertilization. 

Pedicel  (a  little  foot).    The  stalk  upon  which  a  structure  is  borne. 

Peduncle  (a  little  foot).   The  flower  stalk. 

Pentacyclic  (five  cycles).  Applied  to  flowers  whose  four  kinds  of 
floral  organs  are  in  five  cycles. 

Perianth  (around  the  flower).  The  floral  envelopes  or  leaves  of  a 
flower,  taken  collectively;  and  an  analogous  envelope  of  the  sporogo- 
nium  of  certain  liverworts. 

Periblem  (a  cloak).  A  name  given  to  that  part  of  the  meristem  at 
the  growing  point  of  the  plant  axis,  which  lies  just  beneath  the  epider- 
mis and  develops  into  the  cortex. 

Pericambium  (surrounding  growing  tissue).  In  roots,  the  external 
layer  of  the  fibrovascular  cylinder. 

Pericarp  (around  the  fruit).  The  wall  of  the  ovary,  developed  into  a 
part  of  the  fruit. 

Perigynous  (around  the  ovary).  Applied  to  those  flowers  whose  sta- 
mens and  perianth  arise  from  around  the  wall  of  the  ovary. 

Peristome  (around  the  mouth).  In  mosses,  usually  bristle-like  or 
tooth-like  structures  surrounding  the  orifice  of  the  capsule. 

Petal  (a  leaf).   A  corolla  leaf. 

Petiole  (a  little  foot).   The  stalk  of  a  leaf. 

Phanerogamia  (evident  marriage).  A  primary  division  (the  highest) 
of  plants,  named,  from  their  mode  of  reproduction,  the  seed-producing 
plants.  Phanerogam  is  the  English  equivalent. 

Phloem  (the  inner  bark).  The  bark  or  bast  portion  of  a  fibrovas- 
cular bundle. 

Photosynthesis  (light  construction).  The  name  applied  to  the  process 
by  which  chloroplasts  under  the  influence  of  sunlight  manufacture  such 
carbohydrates  as  sugar  and  starch  from  water  and  carbon  dioxide. 


GLOSSARY  529 

Phycocyanin  (seaweed  blue).  A  bluish  coloring  matter  found  within 
certain  algae. 

Phyllotaxy.    Leaf  arrangement. 

Pinna  (a  feather)  ;  pi.  pinnae.  One  of  the  primary  divisions  of  a  pin- 
nate leaf,  as  in  ferns. 

Pinnate.  Having  the  veins  or  the  divisions  of  the  leaf  arranged  in 
rows  on  each  side  of  the  midrib,  as  in  black  locust  (Robinia). 

Pinnule  (a  little  feather).    One  of  the  divisions  of  a  pinna. 

Pistil  (a  pestle).    A  simple  or  compound  carpel  in  spermatophytes. 

Placenta ;  pi.  placentae.  That  portion  of  the  ovary  which  bears  the 
ovules. 

Plerome  (that  which  fills).  A  name  given  to  that  part  of  the  meri- 
stem,  near  the  growing  points  of  the  plant  axis,  which  forms  a  central 
shaft  or  cylinder  and  develops  into  the  axial  tissues. 

Plumule  (a  little  feather).  The  terminal  bud  of  the  embryo  above 
the  cotyledons. 

Pod.    A  dry,  several-seeded,  dehiscent  fruit. 

Pollen.    The  spores  developed  in  the  anther. 

Pollen  tube.  The  structure  that  develops  from  the  wall  of  the  micro- 
spore  of  spermatophytes  and  carries  male  cells  to  the  egg. 

Pollination.    The  transfer  of  pollen  to  the  stigma. 

Polypetalous  (many  petals).  Applied  to  flowers  that  have  their  petals 
free  from  one  another. 

Prosenchyma.  Tissue  composed  of  elongated  cells,  with  tapering  ends 
which  overlap. 

Prothallium  (a  forerunning  shoot)  ;  pi.  prothallia.  The  small,  usually 
short-lived  plant  which  develops  from  the  spore  and  bears  the  sex  organs. 

Protonema  (that  which  is  first  sent  out)  ;  pi.  protonemata.  In  mosses, 
the  filamentous  growth  which  is  produced  by  the  spores,  and  from  which 
the  leafy  moss  plant  is  developed. 

Protoplasm  (that  which  is  first  formed).    The  living  matter  of  cells. 

Pubescent.    Downy,  with  fine  hairs. 

Pyrenoid  (kernel  formed).  Minute  colorless  bodies  embedded  in  the 
chlorophyll  structures  of  some  lower  plants. 

Receptacle.  That  portion  of  an  axis  or  pedicel  (usually  broadened) 
which  forms  a  common  support  for  a  cluster  of  organs,  either  sex  organs 
or  sporophylls. 

Respiration.  The  series  of  processes  by  which  plants  obtain  energy 
through  breaking  down  of  protoplasm  or  food.  Usually  oxygen  is  used 
and  carbon  dioxide  is  formed  as  a  result  of  the  process. 

Reticulated  (net-like).    Having  a  net-like  appearance. 

Rhizoid.  Root-like ;  a  name  applied  to  the  root-like  hairs  found  in 
bryophytes  and  pteridophytes. 


530  PRACTICAL  BOTANY 

Rhizome.    See  Rootstock. 

Rootstock.  A  horizontal,  more  or  less  thickened,  root-like  stem,  either 
on  the  ground  or  underground. 

Saprophyte.  An  organism  that  obtains  its  food  from  dead  or  decay- 
ing organisms. 

Scalariform  (ladder  form).  A  name  applied  to  ducts  with  piths  hori-. 
zontally  elongated,  and  so  placed  that  the  intervening  thickening  ridges 
appear  like  the  rounds  of  a  ladder. 

Scale  (a  flight  of  steps).  Any  thin  scarious  body,  as  a  degenerated 
leaf,  or  flat  hair. 

Sclerenchyma.  A  tissue  composed  of  cells  that  are  thick-walled,  often 
extremely  so. 

Seed.    The  matured  ovule. 

Sepal.    A  calyx  leaf. 

Seta ;  pi.  setae.  A  bristle,  or  bristle-shaped  body ;  in  mosses,  the  stalk 
of  the  capsule. 

Sexual  spore.    One  formed  by  the  union  of  cells. 

Sheath.    A  thin  enveloping  part,  as  of  a  filament,  leaf,  or  resin  duct. 

Sieve  cells.  Cells  belonging  to  the  phloem,  and  characterized  by  the 
presence  of  perforated  plates  in  the  wall. 

Sorus  (a  heap)  ;  pi.  sori.  In  ferns,  the  groups  of  sporangia,  constitut- 
ing the  so-called  "  fruit  dots  " ;  in  parasitic  fungi,  well-defined  groups 
of  spores,  breaking  through  the  epidermis  of  the  host. 

Sperm,  or  Spermatozoid  (animal-like  sperm).   The  male  gamete. 

Spermatophytes  (seed  plants).  The  highest  great  group  of  plants,  of 
which  a  characteristic  structure  is  the  seed. 

Spike.  A  flower  cluster,  having  its  flowers  sessile  on  an  elongated 
axis. 

Spikelet  (diminutive  of  spike).  A  secondary  spike;  in  grasses,  the 
ultimate  flower  cluster,  consisting  of  one  or  more  flowers  subtended  by 
a  common  pair  of  glumes. 

Sporangium  (spore  vessel) ;  pi.  sporangia.  The  spore-producing 
structure. 

Spore  (seed).  Originally  used  as  the  analogue  of  seed  in  flowerless 
plants ;  now  applied  to  any  one-celled  or  few-celled  body  which  is  sepa- 
rated from  the  parent  for  the  purpose  of  reproduction,  whether  sexually 
or  asexually  produced ;  the  different  methods  of  its  production  are  in- 
dicated by  suitable  prefixes. 

Sporogonium  (spore  offspring) ;  pi.  sporogonia.  The  whole  structure 
of  the  spore-bearing  stage  of  bryophytes. 

Sporophyll.    A  leaf  that  bears  sporangia. 

Sporophyte  (spore  plant).  The  asexual  or  spore-producing  stage  of 
an  alternating  plant 


GLOSSARY  531 

Stamen.    The  microsporophyll  in  spermatophytes." 

Stigma.  That  portion  of  the  surface  of  a  pistil  (without  epidermis) 
which  receives  the  pollen. 

Stigmatic.    Relating  to  the  stigma,  or  stigma-like. 

Stoma  (a  mouth)  ;  pi.  stomata.  Epidermal  structures  which  serve  for 
facilitating  gaseous  interchanges  with  the  external  air,  and  for  transpi- 
ration of  moisture.  They  are  often  incorrectly  called  w  breathing  pores." 

Strobilus.    A  cone-like  cluster  of  sporophylls. 

Style.  The  usually  attenuated  portion  of  the  pistil  which  bears  the 
stigma. 

Succulent.    Thick  and  fleshy. 

Suspensor.  A  chain  of  cells  which  develops  early  from  the  oospore, 
and  serves  to  push  the  embryo  cell  deep  within  the  embryo  sac. 

Symbiont.  One  of  the  organisms  that  has  entered  into  a  symbiotic 
relationship. 

Symbiosis  (living  together).  Applied  to  a  condition  in  which  two  or 
more  organisms  are  living  in  an  intimate  relationship. 

Sympetalous.  Having  the  petals  apparently  all  united,  as  if  grown 
together  by  their  edges. 

Syncarpous  (carpels  united).  Applied  to  those  conditions  in  which 
the  carpels  have  united  into  a  compound  pistil. 

Synergids  (helpers).  The  two  nucleated  bodies  which  accompany  the 
oosphere  in  the  embryo  sac,  and  together  with  it  form  the  egg  apparatus. 

Testa  (a  shell).    The  outer  seed  coat. 

Tetracyclic  (four  cycles).  Applied  to  those  flowers  in  which  there  are 
four  cycles  of  floral  organs. 

Tetradynamous  (four  strong).  Said  of  a  stamen  cluster  in  which  there 
are  four  long  and  two  shorter  stamens. 

Thalloid.    Thallus-like. 

Thallus  (a  young  shoot).  The  body  of  lower  plants,  which  exhibits 
no  differentiation  of  stem,  leaf,  and  root. 

Tissue.  A  texture  built  up  of  mutually  dependent  cells  of  similar 
origin  and  character,  as  the  cambium  layer. 

Tracheid.  A  long,  slender  cell,  with  closed  ends  and  its  walls  thick- 
ened after  the  cell  has  attained  its  full  size,  as  in  the  pitted  cells  of 
coniferous  wood. 

Transpiration.  The  loss  of  water  derived  from  the  interior  of  the 
plant  body  in  the  form  of  vapor.  The  term  is  not  generally  used  with 
reference  to  plants  of  low  organization. 

Trichome  (a  hair).  A  general  name  for  a  slender  outgrowth  from  the 
epidermis,  usually  arising  from  a  single  cell. 

Turgidity.  The  normal  swollen  condition  of  active  cells  which  results 
from  the  distension  brought  about  by  absorption  of  water. 


532  PRACTICAL  BOTANY 

Unisexual.    Having  only  male  or  only  female  reproductive  organs. 

Vein.  One  of  the  fibrovascular  bundles  of  leaves  or  of  any  flat  organ 
of  plants. 

Venation.    The  mode  of  vein  distribution. 

Xerophyte.  A  plant  capable  of  thriving  under  conditions  of  strongest 
transpiration  and  with  scanty  water  supply. 

Xylem  (wood).  The  wood  (inner)  portion  of  the  fibrovascular  bundle. 

Zoospore  (animal  spore).    A  motile  asexual  spore. 

Zygomorphic.  Said  of  a  flower  which  can  be  bisected  by  only  one 
plane  into  similar  halves,  bilaterally  symmetrical. 

Zygospore  (yoke  spore).  The  spore  formed  by  conjugation  of  similar 
gametes. 


INDEX 


(References  to  illustrations  are  indicated  by  asterisks  accompanying  page  num- 
bers. When  an  asterisk  precedes  the  citation  of  a  group  of  pages  it  means  that 
several  illustrations  are  included.) 


Absorption  of  carbon  dioxide,  15, 16 

Absorption  of  water  by  roots,  7-9 

Acacia,  flower  of,  353* 

Acacia,  leaf  of,  66* 

Accessory  buds,  92,  93* 

Acorns,  sprouting,  403* 

Actinomorphic,  108,  109* 

Adventitious  buds,  92 

Aerial  roots,  30,  31*,  32* 

Agaricus,  249 

Agave,  75,  76*,  77* 

Agriculture,  3, 159, 167, 434-459.  See 

also    under    Plant   Breeding  and 

Weeds 

Ailanthus  fruit,  150* 
Air,  relation  to  germination,  139, 140 
Air  chamber,  14* 
Air  passages,  29,  30 
Air  plants,  31*,  32,  33,  381,  382,  489* 
Air  roots,  30,  31*,  32*,  33 
Air  storage,  76 
Akene,  328 
Albugo,  223 

Albuminous  substances.  See  Proteins 
Alfalfa,  nitrogen  production  by,  37 
Alga-fungi,  *213~225 
Alga-fungi,  summary  of,  223,  224 
Algae,  159,  *  180-212 
Algae,  classification  of,  212 
Alsophila,  276 
Alternate  leaves,  65,  56* 
Alternation  of  generations,  263-265 
Ament.   See  Catkin 
Angiosperm,  life  history  of,  328,  329 
Angiosperm  flower,  20,  21,  104-114, 

*322-328 

Angiosperms,  158,  *321-334 
Angiosperms,  summary  of  life  cycle, 

329 

Animal  food,  plant  sources  of ,  2, 1 7, 82 
Annual  growth,  definite,  95,  304 
Annual  growth,  indefinite,  95 
Annual  ring,  12,  60*,  61,  304 
Annuals,  12,  33,  34 


Anther,  20*,  21,  110*,  323 

Anther,  modes  of  opening,  111* 

Antheridium,  201,  261*,  269*,  284* 

Anthoceros,  272*,  273,  285 

Anthrax,  165,  171 

Antipodal  cells,  21*,  117*,  325 

Antitoxins,  172,  173 

Apetalous,  106* 

Apple,  leaf  arrangement  of,  66* 

Apples,  454*,  459,  460,  494 

Aquatic  plants,  *479-481 

Arbor  vitse,  310*,  312 

Archegonium,  260*,  270*,  285*,  306* 

Aristolochia  stem,  cross  section  of, 

45* 

Arrangement  of  leaves,  *55-60 
Arrowhead,  478* 
Ascocarp,  230*,  231 
Ascomycetes,  *226-234 
Ascophyllum,  207 
Ascospores,  228 
Ascus,  228,  230* 
Asexual  generation,  264 
Asexual  reproduction,  194 
Asparagus  flower,  109* 
Asparagus  rust,  245 
Associations,  plant,  455,  495,  496 
Avens,  fruit  of,  164* 
Axil,  92* 
Axillary  bud,  92* 
Axillary  inflorescence,  515* 

Bacteria,  36,  37,  161-179,  162* 

Bacteria,  classification  of,  179 

Bacteriology,  159 

Bald  cypress,  distribution  map,  504* 

Balsam,  wild,  flowers  of,  130* 

Balsam,  wild,  fruits  of,  163* 

Bamboo,  337 

Banana,  349*,  360 

Barberry,  245 

Bark,  46,  50* 

Barley,  465,  457 

Basidia  fungi,  226,  240 


633 


534 


PRACTICAL  BOTANY 


Basidiomycetes,  226,  *240-256 

Bast,  hard,  47* 

Bast,  soft  (sieve  tubes),  80 

Batrachospermum,  209* 

Bean  seed,  22*,  136* 

Bean  seeds  and  pod,  development  of, 

22* 

Beech,  one-sided  pruning  of,  42* 
Beech  seedlings,  23* 
Bees,  123 

Begonia,  flowers  of,  108* 
Begonia,  leaf  mosaic  of,  59* 
Berries,  460,  461 
Biennial,  33,  34 
Big  tree,  304*,  311*,  313* 
Bilaterally  symmetrical  flowers,  108, 

109* 
Birch,  flowers  and  flower  clusters  of, 

351* 

Bird  pollination,  130 
Bisexual,  131 
Black  knot,  234 
Black  walnut,  buds  of,  90* 
Blackberry,  430,  461 
Bladderwort,  481* 
Blade  of  leaf,  10*,  13*,  *55-71 
Bleeding,  9 
Blueberry,  364 
Blue-green  algae,  *180~187 
Blue-green    algse,    classification   of, 

187 

Bluets,  flowers  of,  133* 
Bordeaux  mixture,  222.  See  Spray  ing 
Botany,  economic,  definition  of,  159 
Botany,    systematic,    definition    of, 

159 

Botrychium,  288*,  290 
Box  elder,  buds  of,  93* 
Bract,  515* 

Branches,  origin  of,  52*,  53* 
Branching  and  leaf  arrangement,  56 
Breeding,  plant,  *412-433 
Brown  algse,  *206-209 
Brown  rot,  227,  228 
Bryophytes,  158,  257,  273 
Bryophytes,  classification  of,  273 
Bryophytes,  evolution  of  plants,  330, 

334 

Bryophytes,  summary  of,  272,  273 
Buckeye,  bud  of,  91* 
Buckwheat,  flower  of,  106*,  124* 
Budding,  87*,  88 
Buds,  *90-102 
Buds,  adventitious,  92 
Buds,  naked,  90 


Buds,  opening  of,  99,  100 

Buds,  position  of,  92 

Buds,  structure  of,  91*,  95*,  96* 

Bud-scale  scar,  92*,  98*,  100*,  102* 

Bud-scales,  90,  91*,  95*,  96* 

Bulb,  73,  74*,  83 

Bundles,  fibrovascular,  11*,  12 

Burbank,  Luther,  430 

Burs,  146*,  154* 

Cacao,  359,  360 

Cactus,  81*,  482 

Calcium,  448 

Calyx,  20*,  104* 

Cambium,  45*,  304 

Cambium  layer,  45*,  46 

Camembert  cheese,  231 

Camphor  tree,  362* 

Cancer  root,  383* 

Canna,  leaf  of,  336* 

Canning,  169 

Capsule,  153* 

Caraway,  flower  and  fruit  of,  359* 

Carbohydrates,  16 

Carbon,  16 

Carbon  dioxide,  15,  16,  19 

Carbon  dioxide,  absorption  of,  15-17 

Carboniferous  Period,  296 

Carnation  rust,  245 

Carnivorous  plants,  381,  *385-388 

Carpel,  105*,  111 

Carrot  fruit,  359* 

Cascade  Range,  511 

Cassava,  356,  357 

Cassia,  flower  of,  353* 

Casuarina,  484* 

Catalpa,  hardy,  405* 

Catkin,  106*,  107*,  516* 

Cattleya,  31* 

Cedar,  312*,  313 

Cedar  apples,  246*,  247* 

Cell,  8* 

Cell  turgor,  9,  10 

Cell  wall,  8* 

Central  cylinder,  24* 

Central  placenta,  112* 

Century  plant,  75,  76*,  77*,  482 

Century  plant,  section   of  leaf   of, 

483* 

Cereals,  339,  340*,  455-458 
Cetraria,  239 
Channels  for  carrying  plant  food, 

80,  81 

Chaparral,  512 
Chara,  204,  205,  207* 


INDEX 


535 


Cherries,  462 

Cherry,  wild  black,  fruits  of,  155* 

Chestnut  sprouts,  404* 

Chlorophycese,  *  188-206,  212 

Chlorophyll,  14,  181 

Chlorophyll  bodies,  14* 

Chloroplast,  14*,  189 

Chocolate,  359,  360 

Choripetalous,  110 

Choripetalous    dicotyledons,    *350- 

362 

Chorisepalous,  110 
Cilium,  190 

Citrous  fruits,  430,  431,  462,  463 
Cladonia,  237*,  238* 
Cladophora,  194-197 
Cladophyll,  41* 
Classification,  156,  158 
Clavaria,  252* 
Claviceps,  233* 
Clay,  435 

Cleistogamous  flowers,  133,  134* 
Clerodendron,  flowers  of,  132* 
Climbing  plants,  41/60*,  61*,  62*, 

63*,  380,  381 

Climbing  stems,  45*,  49,  *60-63 
Closed  bundles,  54 
Clover,  nitrogen-fixing  by,  37.  *374- 

377,  449 
Clover  leaf,  64* 
Clover  seed,  471,  472 
Club  moss,  293,  294* 
Coal,  297,  298 

Coal-forming  periods,  291,  296,  297 
Cocklebur,  467* 
Coco  palm,  340*,  341*,  343 
Ccenocyte,  195,  199,  215 
Coffee,  367*,  368* 
Coleochaete,  204,  206* 
Collenchyma,  47*,  49* 
Colors  of  flowers,  125,  126 
Columella,  216* 
Coming  true  from  the  seed,  413,  417, 

425 
Comparison  of  great  groups,   330- 

334 

Compass  plants,  64 
Competition,  148-151 
Composite  family,  *368-370 
Compound  cyme,  518* 
Compound  pistil,  112* 
Compound  umbel,  517* 
Cone,  292,  294,  301* 
Cones  of  gymnosperms,  310*,  311* 
Confervas,  204 


Conidia,  221 
Coniferales,  311,  320 
Coniferous  forest,  314*,  315* 
Coniferous  woods,  316,  390* 
Conifers,  industrial  importance  of, 

313,  316 

Conjugation,  194 
Coppice,  403,  404* 
Coprinus,  253 
Cork,  46 

Corn,  cultivation  of,  37,  448,  456,  457 
Corn,  fibrovascular  bundles  of,  11* 
Corn,  grain  of,  419* 
Corn,  root  system  of,  7* 
Corn  breeding,  *419-424 
Corn  cockle,  467* 
Corn  smut,  242*,  373 
Corn  stem,   structure   of,    11*,    12, 

54* 

Corolla,  20*,  104* 
Cortex,  12*,  45*,  49*,  54* 
Cotton,  458,  459 
Cotton  wilt,  234 
Cottonwood  branches  destroyed  by 

sleet,  43* 
Cottonwood  buds,  development  of, 

98*,  99* 
Cottonwood  leaf,  network  of  veins, 

10* 
Cotyledon,   136*,   137*,   139*,   142*, 

143*,  144 

Cover  (operculum),  262 
Cranberry,  363* 
Cranberry-gall  fungus,  223 
Cranesbill,  fruit  of ,  153* 
Cratsegus  bud,  section  of,  96* 
Cross  pollination,  122,  422*,  423 
Crowberry,  rolled-up  leaf  of,  482* 
Cruciferae,  diseases  of,  223 
Cryptogams,  323 

Cup  (cupule)  of  Marchantia,  268* 
Cuticle,  483* 
Cutinized,  484* 
Cyanophyceae,  *180-187 
Cycadales,  311,  *316-318 
Cycads,  *316-318 
Cycas,  317 
Cycloloma,  475* 
Cyme,  518* 
Cypress,  29*,  312 
Cypripedium,  346*,  347* 
Cystopteris,  286* 
Cystopus,  223 
Cytology,  159 
Cytoplasm,  8,  181, 189 


536 


PRACTICAL  BOTANY 


Dahlia,  thickened  roots  of,  34* 

Daily  movements  of  leaves,  *64-66 

Damping  off,  223 

Dandelion,  27 

Dandelion,  fruits  of,  147* 

Darwin,  Charles,  148 

Dasya,  211* 

Date  palm,  344 

Decay,  166,  167 

Deciduous,  19,  66,  68,  302 

Definite  annual  growth,  95 

Dehiscence,  323 

Denitrification,  377 

Dependent  habit,  213 

Dependent  plants,  *371-388 

Desert  plants,  35,  156,  508,  509* 

Deserts  of  United  States,  508 

Desmids,  204* 

Desmodium,  355* 

Desmodium,  fruits  of,  154* 

Determinate  inflorescence,  519 

Diadelphous,  111 

Diagrams,  floral,  114* 

Diastase,  145 

Dichogamy,  131*,  132* 

Diclinous,  106* 

Dicotyledonous  stem,  cross  section 
of,  12*,  45*,  49*,  50* 

Dicotyledonous  stem,  gross  structure 
of,  12*,  *48-53 

Dicotyledonous  stem,  minute  struc- 
ture of,  *44-48 

Dicotyledonous  stem,  rise  of  water 
in,  11 

Dicotyledons,  12,  327 

Dicotyledons,  families  of,  *350-370 

Diffuse  porous  wood,  392* 

Diffusion,  79,  80 

Dimorphous  flowers,  132,  133* 

Dioecious,  106*,  107* 

Dionsea,  387* 

Diphtheria,  172,  173 

Disease,  171,  172,  173,  174,  176 

Disk  flowers,  369* 

Distribution  of  plants,  1,  *494-513 

Distribution  of  seeds,  *146-155 

Diurnal  position,  *64-66 

Dodder,  36,  383,  384,  466* 

Dogtooth  violet,  83*,  345 

Double  fertilization,  *324,  326 

Douglas  fir,  315* 

Downy  mildew,  219*,  222 
Dragon  root,  342* 

Drainage,  436,  437-439 
Draparnaldia,  204* 


Dry  fruits,  151 
Dry-land  farming,  440 
Duckweed,  477* 
Duct.   See  Vessels 
Dunes,  500* 

Earth  star,  254 

Earthworms,  437 

Eastern  and  central  forest  region 

*503-505 

Ecological  groups,  479,  480 
Ecology,  plant,  definition  of,  118, 

119,  159 

Ecology,  summary  of,  *477-513 
Economic  botany,  159 
Ectocarpus,  208 
Edible  seeds,  dispersal  of,  155 
Egg  apparatus,  21*,  117*,  *324 
Egg  cell,  117*,  201 
Elater,  270,  292* 
Elder  stem,  structure  of,  49* 
Elementary  species,  417 
Elm,  flowers  and  flower  clusters  of, 

352* 

Elm  buds,  96*,  97* 
Elm  fruit,  150* 
Embryo,   118,  *136-139,  284,  309*, 

327* 

Embryo  sac,  21*,  117* 
Endosperm,  118,  *136-139,  325* 
Endosperm  nucleus,  117*,  325* 
Energy,  source  of,  in  plants,  19 
Enzymes,  116,  144,  145 
Epidermis,  14*,  24*,  45*,  46,  483*, 

484 

Epigynous,  114 
Epiphytes,  381,  382 
Equisetineae,  291 
Equisetum,  *291-293 
Ergot,  233,  234 

Erosion,  28,  407,  408,  *441-446 
Eryngium  flower  stalk,  structure  of, 

49* 

Esparto,  337 
Euphorbia,  356*,  485* 
Evening  primrose,  flowers  of,  113* 
Evening  primrose,  fruits  of,  153* 
Evening  primrose,  rosettes  of,  57* 
Evergreen,  302 
Evolution  of  plants,  330,  334 
Evolution  of  sex,  197 
Excretion  of  water,  18 
Excretions,  166,  167,  172 
Existence,  struggle  for,  148-151 
Explosive  fruits,  153* 


INDEX 


537 


Fairy  ring  toadstool,  249,  250* 

Fall  of  the  leaf,  19,  66,  68 

Family,  158 

Fermentation,  145,  232,  233 

Ferments,  36 

Fern  gametophyte,  282*,  283* 

Fern  leaflets,  280* 

Ferns,  *274-291 

Fertilization,  201,  325*,  326 

Fertilization,  in  angiosperms,  116*, 

117*,  118 
Fertilizers,  209 
Fibers,  47*,  48* 
Fibers,  commercial,  348,  361 
Fibrovascular  bundles,  11*,  12,  46*, 

54* 

Filament,  110,  111* 
Filicineae,  274 
Fission  plants,  159 
Fleshy  fruits,  uses  of,  155* 
Fleshy  roots,  34*,  35 
Floating  seeds,  154 
Floral  diagrams,  114* 
Floral  organs,  20* 
Flower,  20*,  21,  *104-114,  322 
Flower,  definition  of,  104 
Flower,  morphology  of,  104,  *323~327 
Flower,  organs  of,  20*,  21,  *104-112 
Flower,  plan  of,  105*,  106*,  114* 
Flower,  symmetry  of,  108,  109* 
Flower  buds,  94*,  95,  96 
Flowering  plants,  156 
Flowers,  ecology  of, .*!  18-135 
Flytrap,  Venus,  387* 
Food,  raw  materials  for,  15,  447,  448 
Food,  storage  of,  in  root,  33,  34*,  35 
Food,  storage  of,  in  stem,  77-79 
Food,   transportation    of,  in  plant, 

78-81 

Food  cycle,  15-17 
Food  in  embryo,  *137-139 
Food  manufacture,  15-17 
Forest,  strata  of  vegetation  in,  490- 

492 

Forest  fires,  409,  441,  443 
Forest  map  of  United  States,  510* 
Forestry,  *398-411 
Forests,  pure  and  mixed,  399 
Formations,  plant,  495 
Fossil  plants,  295-297,  318,  319 
Foxglove,  leaf  of,  336* 
Fruit,  *1 50-155 
Fruit  bud,  94*,  95,  96 
Fruit  scars,  101 
Fruit  spurs,  94*,  95,  96 


Fruits,  edible,  *348-350,  351 

Frullania,  *271 

Fucus,  207,  208 

Fuel  value  of  wood,  395 

Funaria,  265 

Fungi,  159,*213-256 

Fungi,  classification  of,  225,  256 

Fungi,  origin  of,  215 

Funiculus,  139 

Fusarium,  432 

Gamete,  194 

Gametophyte,  263-265 

Gamopetalous,  110 

Garnosepalous,  110 

Garden  vegetables,  464 

Gardening,  167,  451,  464 

Geaster,  254 

Gelatinous  foods,  209 

Generations,  alternation  of,  263-265 

Generative  cells  in  pollen  tube,  116* 

Generative  nucleus,  116* 

Genus,  156 

Geography,  plant,  of  the  United 
States,  *503-513 

Geranium  (Pelargonium)  cutting,  5* 

Geranium  leaf,  section  of,  14* 

Geranium  leaf,  surface  view  of,  13*, 
70* 

Geranium  (Pelargonium)  stem,  cross 
section  of,  12* 

Germ  diseases,  161-179 

Germination,  chemical  changes  dur- 
ing, 144,  145 

Germination,  conditions  for,  139, 140 

Germination,  preparation  for,  140, 
141 

Gigartina,  210* 

Gills,  248*,  249* 

Ginger,  wild,  58* 

Ginkgo,  318* 

Ginkgoales,  311,  318* 

Ginseng,  358* 

Glceocapsa,  180,  181,  182 

Glceotrichia,  186,  187 

Gnetales,  311,  318 

Gourd  family,  370 

Grafting,  87,  88*,  89,  462 

Grain,  138*,  139* 

Grape  mildew,  *219-222 

Grapefruit,  462 

Grapes,  463,  464 

Grass  family,  *336-340 

Grasses,  *336-340 

Grasses,  culture  of,  458 


538 


PRACTICAL  BOTANY 


Great  Basin,  508 
Green  algae,  *  188-207 
Green  felt.    See  Vaucheria 
Green  slime,  188 
Groups  of  plants,  156,  158 
Growing  point,  52* 
Guard  cells,  13*,  14    - 
Gymnosperm,  life  history  of,  299-311 
Gymnosperm  cones,  310*,  311* 
Gymnosperms,  158,  *299-320 
Gymnosperms,  classification  of,  320 
Gymnosperms  of  past  ages,  318,  319 
Gymnosporangium,  246*,  247* 
Gynecoeum,  111 

Gypsy  moth,  destruction  caused  by, 
411 

Hairs,  root,  7,  8*,  9 

Hairs  on  leaves,  70*,  71,  485,  486 

Half -inferior  ovary,  113 

Halophytes,  497*,  499 

Hard  bast,  47* 

Hard  woods,  *391-393 

Hardwoqd  trees,  350,  351 

Haustoria,  36,  221*,  230,  384 

Hay,  458 

Hays,  W.  M.,  417 

Head,  516*,  517* 

Heartwood,  51 

Heath  family,  363*,  364 

Helophytes,  479 

Helotism,  373 

Helotists,  213 

Hemlock,  310*,  312,  313 

Hepaticae,  257,  273 

Herbs,  35,  90 

Heredity.    See  Coming  true 

Heterocyst,  183 

Heterospory,  295 

Hevea,  357* 

Hickory,  buds  of,  92* 

Hilum,  136* 

Holdfast,  196*,  202*,  206,  208*,  210* 

Holly  wood,  section  of,  392* 

Honeybee,  leg  of,  123* 

Hop,  twining  of,  60* 

Hopkins,  C.  G.,  420 

Horse  nettle,  471* 

Horse-chestnut  buds,  100*,  101* 

Horsetails,  *291-293 

Horticulture,  434,  451-455 

Host,  35,  36 

Humus,  382,  435,  436 

Hyacinth,  bulb  of,  74* 

Hybrid  blackberries,  430 


Hybrid  plums,  430* 

Hybridizing,  *426-431 

Hybrids,  426,  428*,  429*,  430,  431 

Hydnum,  252 

Hydrangea,  11 

Hydrogen,  16 

Hydrophytes,  479.    See  also  Water 

plants 

Hypha,  214* 

Hypocotyl,  136*,  137*,  143* 
Hypogynous,  114 

Iceland  moss,  239 
Immigration  of  plants,  500-503 
Immune,  172,  432 
Imperfect  fungi,  234 
Indefinite  annual  growth,  95 
Independent  plants,  371 
Indeterminate  inflorescence,  519 
Indian  corn,  kernel  of,  419*,  420 
Indian  corn,  light  requirement  of. 

494 
Indian  corn,  structure  of  stem  of. 

11*,  54* 

Indian  corn  breeding,  *4l  7-424 
Indian  corn  culture,  456,  457 
Indian  pipe,  381* 
Indusium,  279*,  280*,  286* 
Industries,  plants  in,  2,  3.    See  also 

under  Agriculture,    Horticulture, 

Fuel,  Fibers,  Timber 
Inferior  ovary,  113* 
Inflorescence,  *515-519 
Inflorescence,  determinate,  519 
Inflorescence,  diagrams  of,  518* 
Inflorescence,  indeterminate,  519 
Insect  pollination,  *123-129 
Insectivorous  plants.     See  Carnivo- 
rous plants 
Insects,    pollen-carrying    apparatus 

of,  123*,  129* 

Insects,  sense  of  smell  of,  124,  125 
Insects,  vision  of,  125,  126 
Integuments,  324* 
Intercellular  spaces,  14*,  479* 
Internode,  100*,  101* 
Invasion,  501,  502 
Involucre,  519 
Iodine  test  for  starch,  78,  79 
Irish  moss,  212 
Iron,  15,  448 
Ironweed,  fruits  of,  152* 
Irrigation,  440,  441 
Irritability  in    plants,   nature   and 

occurrence  of,  388,  389 


INDEX 


539 


Irritability  of  tendrils,  62 
Ivy,  aerial  roots  of,  63* 
Ivy,  relations  of,  to  light,  63* 

Jimson  weed,  365* 

Jordan,  E.  0.,  162,  164,  165,  173 

Juniper,  311*,  313 

Kelps,  208* 
Kerner,  Anton,  71 
Knees,  of  cypress,  29* 
Knots,  53* 

Laminaria,  208* 

Land  plants,  480 

Lateral  buds,  92* 

Leaf,  *13-20,  *55-69,  89 

Leaf,  fall  of,  19,  66,  68 

Leaf,  member  of  plant  body,  39 

Leaf  arrangement,  55*,  56* 

Leaf  blade,  10*,  13 

Leaf  buds,  91 

Leaf  mosaics,  59*,  60 

Leaf  movements,  57,  *63-66 

Leaf  scars,  92*,  100*,  101* 

Leaf  sections,  14* 

Leaf  tendril,  62 

Leafstalk,  10*,  13 

Leafy  liverworts,  271*,  272 

Leaves,  compound,  13 

Leaves,  functions  of,  15-20,  *76-79, 

89 

Leaves,  simple,  13 
Leaves,  structure  of,  14* 
Leaves,  submerged,  481* 
Legume,  353,  354* 
Leguminous  plants,  36,  37,  *374-377 
Lemon,  462 
Lenticels,  102*,  103* 
Leucoplasts,  79 
Lianas.    See  Climbing  plants 
Lichens,  226,  *235-239 
Lichens,  nature  of,  235-239 
Lichens,  uses  of,  237-239 
Lichens  and  soil  formation,  235, 236, 

238 

Liebig,  Justus  von,  26 
Light,  exposure  to,  55*,  57*,  59* 
Light,  movements  caused  by,  63* 
Light  requirements,  489-494 
Lilac  mildew,  229*,  230* 
Lily  family,  345*,  346 
Lime,  37 
Limnophila,  480* 
Linden,  fruit  cluster  of,  161* 


Litmus,  239 

Liverworts,  158,  257,  *266-272 

Locules,  112* 

Locust,  black,  65,  501,  502 

Lycoperdon,  253* 

Lycopodineae,  293 

Lycopodium,  *293-295 

Macrocystis,  208 

Madder  family,  367*,  368* 

Magnesium,  448 

Male  cells  of  pollen  tube,  116*,  326 

Male  nuclei  of  pollen  tube,  116* 

Mallows,  pollination  in,  121*,  131* 

Malting,  145 

Mangrove,  497* 

Maple  fruit,  150* 

Maple  sugar,  82 

Marchantia,  *266-271 

Marl,  205 

Marsilia,  290*,  291 

May  apple,  72* 

Mechanics  of  stem  and  root,  48,  49*, 

50 

Medullary  ray,  50*,  81 
Megasporangium,  295,  306 
Megaspore,  295,  306,  325 
Mendel's  law,  426 
Mesocarpus,  204* 
Mesophytes,  480,  487,  488 
Mesquite,  root  system  of,  27 
Messmates,  35 
Micropyle,  21*,  117*,  324 
Microsphsera,  229*,  230* 
Microsporangium,  295,  306 
Microspore,  295,  306,  325 
Microsporophyll,  295,  307* 
Migula,  W.,  162 
Mildews,  *219-222 
Milk  supply,  169,  175,  177 
Mineral  constituents  of  plants,  15, 

448 

Mint  family,  364 
Mississippi  River,  delta  of,  28 
Mississippi  River,  silt  carried  by,  28 
Mistletoe,  36,  384* 
Mixed  buds,  91,  94* 
Molds,  166,  178,  *214-219,  231 
Monadelphous,  111 
Monocotyledonous  stems,  *53-55 
Monocotyledonous  stems,  growth  of, 

in  thickness,  54,  55 
Monocotyledons,  12,  327,  335 
Monocotyledons,  families  of,  *335- 

360 


540 


PRACTICAL  BOTANY 


Monoecious,  107,  108* 

Morchella,  229* 

Morel,  229* 

Morning-glory,  fruits  of,  153* 

Morphology,  159 

Morphology  of  the  flower,  104*,  *323- 

327 

Mosaics,  leaf,  59*,  60 
Moss,  life  history  of,  257*-265 
Mosses,  158,  *257~265 
Mucor,  214-217 
Muehlenbeckia,  40* 
Musci,  273 

Mushroom,  240,  *247~252 
Mustard  seedling,  root  hairs  of,  8* 
Mutations,  412 
Mutualists,  35-38*,  213 
Mycelium,  214 
Mycorrhiza,  38* 
Myrsiphyllum,  41* 
Myxomycetes,  224*,  225 

Naked  buds,  90 

Nectar,  124 

Nectar  glands,  124* 

Nectaries,  124 

Nest  fungi,  255* 

Netted  veining,  336* 

New  Zealand,  displacement  of  na- 
tive plants  in,  501,  502 

Nightshade,  leaf  mosaic  of,  59* 

Nightshade  family,  *364-367 

Nilsson,  Hjalmar,  417 

Nitrification,  36,  37,  374,  377 

Nitrogen,  15,  17,  374-378,  448,  449 

Nitrogen-fixing  bacteria,  374-378, 448 

Nocturnal  position,  *64-66 

Nostoc,  182*,  183,  184 

Nucellus,  117* 

Nucleus,  8* 

Nutrient  substances,  15 

Nutrition  of  plants,  15-17,  36-38,  39, 
40,  *77-81,  160,  *371-388,  447-451 

Oak  leaves  and  acorns,  157* 

Oak  tracheids,  48* 

Oak  trees,  410* 

Oak  wood,  cross  section  of,  50* 

Oat,  root  system  of,  26 

Oat  smut,  240*-242 

Oats,  455,  457 

Odors  of  flowers,  124,  125 

03dogonium,  201*,  202* 

Oil,  138,  144 

Oleander  leaf,  76 


Olive,  vertical  leaves  of,  64* 

Olive  family,  370 

Onion,  seed  and  seedling  of,  137* 

Onoclea,  289* 

Oogonium,  201*,  203* 

Oospore,  201,  203*,  221*,  222*,  261, 

270,  284,  309,  326 
Open  bundles,  54 
Opposite  leaves,  55* 
Orange,  431,  462 
Orchid,  31*,  382 
Orchis  family,  *346-348 
Order,  158 
Origin  of  sex,  197 
Orobanche,  383* 
Oscillatoria,  184,  185*,  186 
Osmosis,  79 
Osmunda,  287* 
Ovary,  112*,  324*,  324 
Ovule,  112*,  306,  324* 
Ovule,  structure  of,  21*,  306*,  324* 
Oxygen,  17*,  19 

Palisade  cells,  14* 

Palm  family,  341 

Palms,  *340-343 

Panicle,  517* 

Parallel  veining,  336* 

Parasites,  35-37,  156,  213,  218,  219, 
222,  223,  226,  229,  234,  240,  241, 
372,  381,  383*,  384* 

Parasitic  bacteria,  378,  379 

Parasitic  roots,  35,  36 

Parasitism,  372 

Parenchyma,  14* 

Parsley  family,  357,  358,  359* 

Parsnip  fruit,  359* 

Parthenogenesis,  219 

Pasteur,  Louis,  165,  178,  233 

Pathology,  159 

Pea  family,  *353-355 

Pea  seedling,  mutilated,  144* 

Peach  flower,  prepared  for  hybridi- 
zation, 427* 

Peach  mildew,  234 

Peach  rot,  228 

Peaches,  461,  462 

Peanut  seedling,  22* 

Peanuts,  crop  of,  354 

Pears,  460 

Peat,  264*,  265 

Peat  bogs,  265 

Peat  moss,  264*,  266 

Pedicel,  519 

Peduncle,  619 


INDEX 


541 


Penicillium,  223,  231* 

Perennial,  12,  33,  35 

Perianth,  109 

Perigynous,  114 

Perisperm,  136 

"Peronospora,  223 

Petal,  20*,  105* 

Petiole,  13 

Peziza,  226,  227 

Pfeffer,  W.,  389 

Phseophycese,  206 

Phallus,  254* 

Phanerogams,  323 

Phloem,  see  Bast 

Phosphorus,  15,  448 

Photosynthesis,  15-17,  39,  40,  181 

Phycomycetes,  *213-225 

Phylloxera,  463,  464 

Physiology,  159 

Phytopathology,  159 

Phytophthora,  222,  223 

Pine  forests,  299 

Pine  needle,  300,  302*,  303* 

Pine  seed,  309* 

Pine  stem,  growth  of,  44,  51,  52 

Pine  wood,  section,  390* 

Pineapples,  348* 

Pmesap,  382* 

Pi  mis,  *299-309,  314 

Pistil,  20*,  21*,  111,  112* 

Pistillate  flower,  106*,  108* 

Pitcher  plants,  386,  387* 

Pith,  11,  12* 

Placenta,  112* 

Plains  region,  505-507 

Plant  associations,  495,  496 

Plant  breeding,  *412-433 

Plant  cell,  7,  8 

Plant  fibers,  47*,  48* 

Plant  food  for  domestic  animals,  2 

Plant  formations,  495 

Plant  geography,  *495~513 

Plant  industries,  *434-464 

Plant  lice,  372,  373 

Plantain,  flowers  of,  131* 

Plants  as  fertilizers,  36,  37 

Plasmopara,  *219-222 

Plastid,  14* 

Pleurococcus,  188,  189*,  190 

Plowrightia,  234 

Plum,  black  knot,  234 

Plums,  430*,  462 

Plumule,  136* 

Poison  ivy,  60* 

Pokeweed,  473* 


Pollen,  115*,  307,  325 

Pollen,  discharge  of,  111* 

Pollen  chamber,  110* 

Pollen   grain,  germination    of,  115 

116*,  117*,  308,  325,  326* 
Pollen  sac,  110*,  111,  307* 
Pollen  tubes,  116*,  117*,  308*,  326* 
Pollen-carrying     apparatus,     123*, 

129* 

Pollination,  *115-135,  307,  326 
Pollution  of  water  supply,  169,  174, 

177,  205,  206 
Polyporus,  *251-253 
Polytrichum,  265 
Pome  fruits,  459,  460 
Pond  lily,  67*,  478* 
Pondweed,  section  of  stem  of,  479* 
Poplar  bud,  section  of,  96* 
Position  of  buds,  92* 
Postelsia,  208 
Potassium,  15,  448 
Potato,  365,  366,  413*,  453* 
Potato  blight,  222,  453* 
Prairies,  506,  507 
Preservation  of  fruits,  168,  169 
Prickly-pear  cactus,  81* 
Pronuba,  128*,  129* 
Propagation  by  cuttings,  86 
Propagation  by  roots,  33* 
Propagation  of  seed  plants,  33*,  *82- 

89,  *139-144 
Proteins,  17,  35,  77,  80, 138, 144, 419- 

421 

Protonema,  257,  259 
Protoplasm,  8*,  181 
Protoplasm,  structure  of,  181 
Pruning,  451-453 
Pruning,  due  to  shade,  42* 
Pteridophytes,  158,  *274-298 
Pteridophytes,  classification  of,  298 
Pteridophytes,  evolution   of  plants, 

330,  334 
Pteridophytes,     summary    of,    297, 

298 

Pteris,  275* 
Ptomaines,  170 
Public  health,  161-179, 169, 174, 177, 

205,  206 

Puccinia,  *243-246 
Puffball,  240,  253,  254 
Pulvinus,  65 
Pythium,  223 

Quercus,  157*,  158 
Quince,  460 


542 


PRACTICAL  BOTANY 


Raceme,  615* 

Radial  symmetry,  108,  109* 

Rafflesia,  384 

Rainfall,  437 

Rainfall  map  of  United  States,  511* 

Ray,  medullary,  50* 

Ray  flowers,  369* 

Receptacle,  105 

Red  algae,  209 

Red  clover,  leaf  of,  64* 

Redwood,  313*,  512 

Regions    of    vegetation    in    United 

States,  *503-513 
Reindeer  moss,  239 
Reproduction,  160,  194 
Reproduction,  sexual,  in  flowering 

plants,  21*,  22*,  *  115-1 18 
Reproduction  by  leaves,  89 
Reproduction  by  portions  of  stem, 

82,  *83-89 
Resin  duct,  303* 
Respiration,  19,  76 
Response,  389 
Resting  buds,  90* 
Rhizoids,  214,  215* 
Rhizopus,  *214-217 
Rhododendron,  69* 
Rhodophycese,  *209-212 
Riccia,  266,  267 
Ricciocarpus,  266* 
Rice,  339,  340*,  455,  458 
Ring,  annual,  50*,  51 
Ring-porous  wood,  391* 
Rise  of  water  in  steins,  11,  80 
Rockweeds,  207* 

Rocky  Mountain  region,  *506~508 
Root,  *5-10,  *24-38 
Root,  dicotyledonous,  section  of,  24* 
Root,  fleshy,  34* 
Root  absorption,  7-9 
Root  climbers,  61,  63* 
Root  hair,  7,  8*,  9 
Root  pressure,  9 
Root  rot,  234 

Root  system,  6*,  7*,  26,  27 
Root  tubercle  bacteria,  374-378, 449 
Root-tubercles.  36,  37 
Roots,  aerial,  30,  31* 
Roots,  air  requirements  of,  29 
Roots,  anchorage  by,  5,  6*,  25 
Roots,  earth,  25,  26 
Roots,  effects  of,  on  soil,  28 
Roots,  parasitic,  35,  36 
Roots,  pull  of,  27 
Roots,  reproduction  by,  33* 


Roots,  storage  of  food  and  water  in, 

33,  34,  35 

Roots,  structure  of,  24*,  49* 
Roots,  water,  30 
Roots,  water-lifting  by,  9 
Rootstock,  72*,  73*,  275*,  276,  277 
Roquefort  cheese,  231 
Rose  family,  352*,  353 
Rose  family,  fruits  of,  459-462 
Rose  mildew,  234 
Rosette  plants,  57*,  58 
Rosin,  316 
Russian  thistle,  148 
Rusts,  240 
Rye,  455,  457 

Sac  fungi,  *226-234 

Saccharomycetes,  232*,  233 

Sagebrush,  508* 

Sago  palm,  317 

Salt  marsh  plants.    See  Halophytes 

Salts,  498,  499 

Saltwort,  499 

Salvinia,  291* 

Sap,  movements  of,  9,  11,  80 

Saprolegnia,  217*,  218* 

Saprophytes,   213,   218,   372,    381*, 

382* 

Saprophytic  bacteria,  374 
Saprophytism,  372 
Sapwood,  51 
Sargasso  seas,  207 
Sargassum,  207 
Sassafras  wood,  section,  391* 
Scaly  buds,  *90~96 
Schizomycetes,  161,  179 
Scion,  88* 
Sclerenchyma,  303* 
Sclerotinia,  *226-228 
Scouring  rush,  291*,  293 
Scramblers,  61 
Scutellum,  139* 
Sea  lettuce,  204  ' 
Seed,  21-23,  *136-141,  309 
Seed,  definition  of,  22,  23,  147,  148 
Seed  coats,  138,  139 
Seed  distribution,  *146~155 
Seed  leaf,  136*,  137* 
Seed  plants,  *5-155,  299,  321 
Seedlings,  22*,  23*,  137*,  *141-145 
Seedlings,  mutilated,  growth  of,  144* 
Seedlings,  types  of,  *1 41-1 43 
Selaginella,  293-295 
Selection  by  plant  breeder,  412,  415, 

416,  421-425,  432 


INDEX 


543 


Self-pollination,  120,  121* 

Self-pruning,  66,  93~95 

Sepal,  20*,  105* 

Sequoia,  304*,  311*,  313* 

Sex,  origin  of,  197 

Sexual  reproduction  in  angiosperms, 

*115-118 
Sexual  spore,  194 
Shade  plants,  489-492 
Shepherd's-purse,  ovule  and  embryo, 

327* 

Shoot,  39 

Short-stemmed  plants,  58* 
Sieve  tubes,  45*,  80 
Simple  pistil,  105*,  112 
Slime  molds,  224*,  225 
Smilax.    See  Myrsiphyllum 
Smilax,  62* 
Smuts,  *240-242,  454 
Snail  pollination,  130 
Snapdragon,  flowers  of,  126* 
Soft  bast  (sieve  tubes),  45*,  80 
Soil,  434-451 

Soil  bacteria,  374-378,  449 
Soil  fertility,  447-451 
Solomon's  seal,  rootstock  of,  73* 
Solomon's  seal,  leaf  of,  336* 
Sorrel,  467* 
Sorus,  280 

Spanish  moss,  381,  382,  489* 
Spanish  needles,  fruits  of,  146* 
Species,  156,  158 
Sperm,  201,  202*,  219,  261*,  269*, 

283,308,318 
Spermatophytes,  158 
Sperinatophytes,  evolution  of  plants, 

330,334 

Sphagnum,  264*,  265 
Spiderwort,  343* 
Spike,  516* 
Spiral  vessel,  46* 
Spirogyra,  *191-193 
Spongy  parenchyma  of  leaf,  14* 
Sporangiophore,  216 
Sporangium,  279*,  281* 
Spore,  190 
Sporidia,  245 
Sporophyll,  290 
Sporophyte,  263-265 
Spraying,  222,  453*,  454,  455 
Spruce,  Douglas,  315* 
Spruce  trees,  6*,  257,  312 
Spur,  fruit,  94*,  95,  96 
Spurge  family,  356*,  357* 
Squash  seed,  section  of,  136* 


Stamen,  20*,  104*,  105*,  110*,  111*, 

307,  323 

Staminate  flower,  106*,  108* 
Starch,  15-17,  35,  77-80,  82,  138, 145 
Starch  in  leaves,  78,  79 
Starch-making,  16 
Stem,  11*,  12*,  *39-55,  74-77,  *80- 

103 

Stem,  dicotyledonous,  minute  struc- 
ture of,  44,  45*,  46*,  47*,  48*,  49* 
Stem,  early  history  of,  52*,  142*,  143* 
Stem,  functions  of,  39-42 
Stem,  monocotyledonous,  53,  54*,  55 
Stem,  rate  of  growth  of,  44 
Stem,  structure  of,  11*,  12*,  *44-54 
Stemless  plants,  58* 
Steins,  climbing,  *60~64 
Stems,  storage  of  food  in,  77 
Stems,  twining,  60*,  61 
Stems,  underground,  72*,  73*,  74* 
Sterilization,  169 
Stiffening,  mechanics  for,  48,  49* 
Stigma,  112*,  324 
Stimulation,  responses  to,  389 
Stipe,  249 
Stipules,  91* 

Stomata,  13*,  14,  303*,  483* 
Stone  fruits,  461,  462 
Stonecrop,  flower  of,  105* 
Stonewort,  205,  207* 
Storage  of  food  in  root,  33,  34*,  35 
Storage  of  food  in  the  seed,  *137-139 
Storage  of  food  in  the  stem,  77 
Strawberries,  460,  461 
Strengthening  tissue,    arrangement 

of,  48,  49* 
Strobilus,  292*,  294* 
Struggle  for  existence,  148-151 
Style,  112*,  324 
Submerged  leaves,  480*,  481* 
Sugar,  15-17,  337,  424 
Sugar,  formed  during  germination, 

145 
Sugar  beet,    light    requirement  of, 

493 

Sugar-beet  breeding,  424,  425 
Sugar  cane,  337,  339* 
Sulphur,  15,  448 
Sumach,  361 
Summer-deciduous  trees  and  shrubs, 

70,  486 

Sun  plants,  489,  492,  493,  494 
Sundew,  385*,  386* 
Sunflower    stem,  cross    section    of, 

45* 


544 


PEACTICAL  BOTANY 


Superior  ovary,  113 

Suspensor,  327* 

Swamp  lands,  436,  438 

Sweet  pea,  flower  of,  109*,  354* 

Sweet  pea,  fruit  of,  354* 

Sweet  potato,  sprouting  of,  33* 

Switch  plants,  39 

Sycamore  wood,  section  of,  392* 

Symbiosis,  35-37,  *372-375 

Symmetry,  108,  109* 

Sympetalous,  110 

Sympetalous  dicotyledons,  *363- 
370 

Synergids,  325 

Synsepalous,  110 

Syringa  (Philadelphus)  leaves,  ar- 
rangement of,  55* 

Systematic  botany,  159 

Taproot,  143* 

Tar,  316 

Taxodium,  29* 

Taxonomy,  definition  of,  159 

Tea,  360* 

Teleutospores,  243 

Temperature  and  germination,  139, 

140 

Tendril,  61*,  62* 
Tendril  climbers,  61*,  62* 
Terminal  bud,  92* 
Terminal  flowers,  518*,  519 
Terrace  farming,  444,  446 
Testa,  136* 
Thallophytes,  classification  of,  187, 

212,  225,  256 
Thallophytes,   evolution  of    plants, 

159,  330,  334 

Thickening  of  stems,  50*,  51,  52 
Thistle,  Russian,  148 
Thuja,  310*,  313* 
Tillage,  439 
Tillandsia,  489*,  490* 
Timber,  *390-397 
Timber  line,  506*,  507* 
Timber  supply,  396,  397 
Timothy,  pistil  of,  119* 
Timothy,  variation  in,  413 
Tissue,  11, 12 
Toadstool,  240,  247-252 
Tobacco,  366 
Tolerant  and  intolerant  trees,  399, 

400 

Tomato,  366 
Toxins,  172 
Tracheids,  48*,  390* 


Transition  from  stamens  to  petals, 

105* 

Transpiration,  18,  *482-487 
Transpiration,  amount  of,  18 
Transplanting,  452 
Transportation  by  water,  155 
Tree  ferns,  276* 
Tree  planting,  *403-405 
Trees,  6*,  26,  29*,  32*,  42*,  43*,  44, 

51-53.    See  also  Forestry 
Trillium,  344* 
Trypsins,  145 
Tube  nucleus,  116* 
Tuber,  73 

Tubercles  on  roots,  36,  37 
Tuberculos's,  162,  171,  174,  175,  176 
Tumbleweeds,  475* 
Turgidity,  9-11 
Turgor,  9-11 
Turpentine,  314*,  316 
Twigs,  fall  of,  66 
Twiners,  60*,  61 
Typhoid,  162,  164,  172,  174,  177 

Ulothrix,  196*,  197 
Ulva,  204 
Umbel,  516* 
Umbellet,  517* 
Underground  stems,  *72~77 
Union  of  carpels,  112 
Union  of  stamens,  110,  111 
Unisexual  flowers,  106*,  107* 
United  States,  plant  geography  of, 

*503-513 
Uredospores,  243 
Usnea,  236,  237,  496* 
Ustilago,  240 

Vaccination,  172 

Vacuole,  189 

Variation,    412-414,   *417-421,  425, 

*428-430 
Variety,  412 

Vaucheria,  195,  *198-201,  215 
Vegetative  reproduction,  33*,  *82- 

89,  187 
Vein,  10* 

Venus' s-fly trap,  387* 
Vernal  grass,  337*,  338* 
Vessel,  46* 
Victoria,  67* 
Vilmorin,  Louis,  424 
Violets,    cleistogamous    flowers    of, 
.  134* 
Virginia  creeper,  61*,  380 


INDEX 


545 


Water,  absorption  by  roots,  7-9 

Water,  amount  transpired,  18 

Water,  movement  of,  9,  11,  80 

Water  ferns,  290*,  291* 

Water  lily,  flower  of,  105* 

Water  molds,  *21 7-219 

Water  plants,  *479-481 

Water  plants,  leaves  of,  67*,  68 

Water  roots,  30 

Water  storage,  74,  75 

Water  supply,  169,    174,    177,   205, 

206 

Water  supply  in  soils,  439-441 
Webber,  H.  J.,  430 
Weeds,  *465-476 
Weeds,  aquatic,  471 
Weeds,  classes  of,  465,  466 
Weeds,  dissemination  of,  472-474 
Weeds,  injuries  caused  by,  470-472 
Weeds,  origin  of,  473 
Weeds,  prevention  of,  475,  476 
Weeds,  success  of,  466-468 
Wheat,  hybridizing  of,  428*,  429* 
Wheat  breeding,  413-417 
Wheat  culture,  457 
Wheat  grain,  section  of,  138*,  139* 
Wheat  rust,  *242-245 
White  pine,  distribution  map,  504* 
Wild  ginger,  58* 
Williams,  C.  G.,  423 
Willow,  flowers  of,  106*,  107* 
Wilting  of  corn  leaves,  6*,  20 
Wind  pollination,  120 


Winged  fruits  and  seeds,  150*,  151* 

Winter  buds,  90* 

Winter  spores  of  wheat,  rust,  *243- 

245 

Wood,  coniferous,  304,  390* 
Wood,  fuel  value  of,  395 
Wood,  physical  properties  of,  392- 

395 
Wood,  structural  advantages  of,  394, 

395 
Wood,  structure  of,  45*,  46*,  48*, 

*50-53 

Wood,  tracheids  of,  48*,  391 
Wood  fibers,  48 

Wood  sections,  50*,  53*,  *390-392 
Wood  sorrel,  leaf  positions  of,  65* 
Woodbine,  61* 

Xerophytes,  480,  *481-487 

Yarrow,  head  and  flower  of,  369* 

Yeast,  232*,  233 

Yellow  fever,  163 

Yellow  pond  lily,  transitions  between 

petals  and  stamens  of,  105* 
Yucca,  509* 
Yucca,  pollination  of,  127, 128*,  129* 

Zamia,  317 
Zoospores,  191 
Zygnema,  204* 
Zygomorphic,  108,  109* 
Zygospore,  194 


ANNOUNCEMENTS 


BERGEN  AND  CALDWELL 
BOTANIES 

By  JOSEPH  Y.  BERGEN  and  OTIS  W.  CALDWELL,  The  University  of  Chicago 


INTRODUCTION    TO    BOTANY     368  pages,  illustrated 

With  Key  and  Flora 
PRACTICAL    BOTANY     545  pages,  illustrated 


THE  Bergen  and  Caldwell  Botanies  have  been  received  with 
enthusiasm  by  teachers  the  country  over.  They  meet  modern 
teaching  conditions,  placing  the  emphasis  on  those  aspects  of 
plant  life  that  are  particularly  worth  while  for  general  knowledge. 
They  give  definite  treatment  to  plant  diseases,  bacteria  and  their 
relation  to  gardening  and  to  sanitation,  forestry,  plant  breeding, 
and  the  application  of  botanical  facts  to  agriculture,  horticul- 
ture, and  other  industries.  At  the  same  time  they  furnish  a  thor- 
ough and  well-proportioned  grounding  in  the  science  of  botany. 

The  text  is  written  for  beginning  students  and  is  always  clear 
and  interesting.  Technical  terms  are  used  sparingly  and  when 
used  are  carefully  explained.  Throughout  the  authors  empha- 
size the  dynamic  side  of  botany.  They  do  not  treat  the  plant 
primarily  as  a  subject  for  dissection  or  for  making  preserved 
specimens,  but  as  an  organism  with  a  living  to  make  under  con- 
ditions sometimes  favorable  and  sometimes  unfavorable. 

The  illustrations  are  numerous,  pertinent,  and  of  unusual 
technical  and  artistic  excellence.  They  are  from  original  draw- 
ings and  photographs  prepared  by  naturalist-artists  expressly 
for  these  books. 

"  Introduction  to  Botany"  offers  a  distinctly  elementary  pres- 
entation for  shorter  courses.  "  Practical  Botany  "  contains  an 
abundance  of  material  for  a  full  year's  work. 


GINN  AND   COMPANY   PUBLISHERS 


TEXTBOOKS   IN   BIOLOGY 

FOR  HIGH  SCHOOLS  AND  COLLEGES 
BOTANY 

Bergen  :    Botanies  (For  list  see  High-School  and  College  Catalogue) 

Bergen  and  Caldwell  :   Introduction  to  Botany 

With  or  without  Key  and  Flora 
Bergen  and  Caldwell  :   Practical  Botany 
Clute:  Agronomy 
Clute  :  Laboratory  Botany 

Clute  :  Laboratory  Manual  and  Notebook  in  Botany 
Densmore  :  General  Botany 
Duggar  :   Fungous  Diseases  of  Plants 
Eikenberry  :   Problems  in  Botany 

Frye  and  Rigg  :   Laboratory  Exercises  in  Elementary  Botany 
Gruenberg  :  Elementary  Biology 
Hodge  and  Dawson  :  Civic  Biology 
Meier  :  Herbarium  and  Plant  Description 
Meier  :  Plant  Study  (Revised  Edition) 
Penhallow  :   Manual  ,of  North  American  Gymnosperms 
Roth:  First  Book  of  Forestry  .  •  _. 

BACTERIOLOGY 

Conn  :  Bacteria,  Yeasts,  and  Molds  in  the  Home  (Rev.  Ed.) 
Reed  :   Manual  of  Bacteriology 

ZOOLOGY 

Linville  and  Kelly  :   Laboratory  and  Field  Work  in  Zoology 

Linville  antl  Kelly  :  Textbook  in  General  Zoology 

Meier  :  Animal  Study 

Pratt:  Course  in  Invertebrate  Zoology  (Rev.  Ed.) 

Pratt  :  Course  in  Vertebrate  Zoplogy 

Sanderson  and  Jackson  :   Elementary  Entomology 

PHYSIOLOGY 

Blaisdell  :  Life  and  Health 
Blaisdell:   Practical  Physiology 
Brown  :   Physiology  for  the  Laboratory 
Bussey  :  A  Manual  of  Personal  Hygiene 
v  Hough  and  Sedgwick  :  The  Human  Mechanism  (Rev.  Ed.) 
Jewett  :  The  Next  Generation 


GINN  AND   COMPANY   PUBLISHERS 


HIGH-SCHOOL  BIOLOGY 

ELEMENTARY  BIOLOGY 

By  BENJAMIN  CHARLES  GRUENBERG,  Head  of  the  Biology  Department, 
Julia  Richman  High  School,  New  York.  8vo,  cloth,  x+  528  pages,  illustrated. 

MANUAL  OF  SUGGESTIONS  FOR  TEACHERS  to  accompany  "  Elemen- 
tary Biology."    J2mo,  cloth,  95  pages,  illustrated. 

HITHERTO  the  knowledge  of  biology  has  been  regarded  as  an  end 
in  itself.  Here  it  is  considered  as  a  weapon  by  means  of  which  man 
may  conquer  his  surroundings.  The  student  learns  not  only  what 
biology  is,  but  how  it  can  be  used.  Application  of  the  principles 
learned  is  immediate  and  practical.  The  problems  presented  and 
suggested  are  such  as  affect  the  welfare  of  individual,  community, 
and  race. 

In  method  the  book  is  inductive.  Pupils  learn  rather  to  observe 
what  plants  and  animals  do  and  how  they  do  it  than  to  memorize 
lists  of  organisms  and  their  functions. 


CIVIC  BIOLOGY 

By  CLIFTON  F.  HODGE,  General  Extension  Division,  University  of  Florida, 
and  JEAN  DAWSON,  recently  head  of  the  Department  of  Biology,  Cleveland 
Normal  School.  8vo,  cloth,  viii  +  381  pages,  illustrated. 

THIS  book  provides  a  well-organized  course  in  high-school  biology 
that  places  the  emphasis  on  the  practical  applications  of  the  subject, 
particularly  to  community  problems.  The  keynote  of  the  whole  argu- 
ment is  united  effort  to  prevent  the  enormous  losses  —  in  destruc- 
tion of  natural  resources,  in  unfruitful  labor,  in  damage  to  property, 
in  preventable  disease  —  now  common  because  of  insufficient  civic 
organization  and  to  preserve  valuable  species  from  extermination. 

i66a 

GINN  AND   COMPANY   PUBLISHERS 


BOOKS   IN   BOTANY 

PLANT  STUDY  (REVISED  EDITION) 

By  W.  H.  D.  MEIER,  Head  of  the  Department  of  Natural  Science  in  the 
State  Normal  School,  Framingham,  Mass. 

Portfolio  containing  36  plant  studies,  with  space  for  drawings,  18  sheets  ruled 
on  both  sides  for  notes,  and  10  sheets  for  description  and  preservation  of 
specimens.  In  Biflex  Binder.  Plant  Study  Sheets  (pages  1-36). 

OFFERS  a  laboratory  and  field  course  in  botany  admirably  designed 
for  students  who  desire  to  make  it  their  final  course,  as  well  as  for  those 
who  intend  to  do  higher  work.  The  material  presented  is  ample  for  stu- 
dents who  take  the  examination  offered  by  the  College  Entrance  Exam- 
ination Board,  and  the  special  examinations  in  botany  given  by  Harvard 
University  and  other  leading  schools.  The  general  facts  of  structure  and 
function,  starting  with  seeds  and  ending  with  fruits,  are  first  studied; 
then  the  life  history  of  plants,  beginning  with  the  lowest  forms.  A 
sufficient  number  of  plant-description  sheets  are  given  to  enable  the 
student  to  become  familiar  with  the  leading  groups  of  flowering  plants. 

LABORATORY  MANUAL  AND  NOTEBOOK  IN 
BOTANY 

By  WILLARD  N.  CLUTE,  Flower  Technical  High  School  for  Girls,  Chicago. 

65+42  blank  pages 

A  COMPREHENSIVE  laboratory  manual  of  botany  on  the  loose-leaf 
plan.  Designed  for  the  first  half-year  in  botany  in  the  high  school, 
it  deals  with  the  structure  and  life  processes  of  the  flowering  plants, 
with  a  brief  survey  of  the  lower  forms  of  vegetation,  such  as  mosses, 
ferns,  and  fungi.  The  course  is  inductive,  and  is  so  arranged  that  the 
pupil  must  see  and  reason  for  himself,  working  out  his  answers  from 
the  study  of  easily  obtained  material. 

LABORATORY  BOTANY 

By  WILLARD  N.  CLUTE,  Flower  Technical  High  School  for  Girls,  Chicago. 

xiv  +  177  pages 

FOR  the  teacher  who  is  crowded  for  time  or  the  student  who  de- 
sires to  do  independent  work,  Clute's  "  Laboratory  Botany  "  will  be 
found  invaluable.  It  is  made  up  of  clear  and  accurate  outlines  of  spe- 
cific subjects,  such  as  root,  stem,  flower,  fungi,  bryophytes,  gymno- 
sperms,  etc. ;  directions  for  examining ;  and  lists  of  definite  questions 
which  will  bring  out  all  the  different  points  of  the  student's  investi- 
gation. It  can  be  condensed  or  extended  at  will. 


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